Troubling Unchildlike Behavior

Shooting a man and threatening others with a gun is just the beginning...

"TWELVE? Twelve years old? You lost your virginity when you were twelve?"

—Arnold J. Rimmer, Red Dwarf

Kids should be kids, at least that's how the saying goes. That means worrying about little kid things and doing little kid things, such as playing on the trampoline, watching TV, going fishing, or whatever it is that kids do locally. What we don't expect kids to do is to drink alcohol, smoke, have sex, use drugs, hitchhike, commit violent crimes, or do other things we associate only with teenagers or adults. Yes, many adults are upset when a teenager drinks beer, but it's disturbing when a 10-year-old does it.

In fiction, there's two ways this tends to occur. Sometimes the kid is shown engaging in such behavior as though it's normal for them, and this can be used to show that the child has had a harsh upbringing. Other times, the kid is trying an "adult" behavior for the first time, which may sometimes have disastrous consequences.

The Creepy Child, the Enfant Terrible and the Evil Orphan draw much of their force from this. From the Mouths of Babes is the Sub-Trope where the child only says troubling unchildlike things.

The Fille Fatale is considered this less than is plausible, since sexual precociousness is often a sign of sexual abuse.

Child Soldiers are a particularly tragic and horrific example of this.

For when kids see things (or have things happen to them) that they shouldn't instead of do things they shouldn't, see Harmful to Minors. A Teenage Wasteland runs on this.

Contrast with Wise Beyond Their Years, which is about positive strangely-adult behavior, and Acting Your Intellectual Age, which is neutral.

Note that if the kid is Really Seven Hundred Years Old and just has the physical appearance of a child, it doesn't count. This is for when actual children are the ones engaging in the unchildlike behavior.

Examples of Troubling Unchildlike Behavior include:

As Though It's Normal for Them

Advertising

This hilarious condom commercial. It shows a five year old getting a tattoo, cutting his teacher's chair with a chainsaw and being stopped by the police after stealing a car. He continuously explains that his mom said he could. It turns out he'd overheard her cry out "Yes! Yes! Yes!" during sex in another room and assumed that she was replying to him.

Anime and Manga

In Full Metal Panic!, Sousuke when he was a kid, as seen in his and Kalinin's backstory. He kills without batting an eye, has an extremely nihilistic view of things, and is creepily unemotional. Especially noticeable here.
After adopting Pinoko, Black Jack is more than a little disconcerted to discover that the 10-day-old (who insists she's a "virgin maiden" of 18 and looks about 6) has developed feelings for him—but what really scares him is that she already knows what a virgin is

Black Jack: Good God, where did you learn that kind of language?

Subverted in Monster. Dieter tosses back a shot like a pro, then jauntily salutes the rest of the patrons as he leaves with a toothpick in his mouth. Once outside, though, he immediately begins retching and questioning the sanity of adults who drink that stuff for fun.
- Also played straight with Johan, who by age 10 had killed several sets of foster parents and calmly and smilingly talked all of Kinderheim 511 into killing each other.
Michio Yuki, the Villain Protagonist of MW, has become this the moment he becomes Ax Crazy by the titular chemical warfare.
Lucy (and to an extent most of the Diclonii) in Elfen Lied are extremely homicidal little girls.
Black Butler has Ciel, an aristocrat living in Victorian London. At the mere age of 13 (he starts off 12, but turns 13 early in the series) he is the head of the household, runs a successful toy and confectioneries company, and is the "Queen's Watchdog" which sends him out on often very dangerous and frightening missions such as helping to catch Jack the Ripper. Personality-wise, he's bitter and jaded... but his darker view on things is because of a traumatic past experience. Still, he's an Improbable Age character. Oh, did I mention he will command his awesome butler to kill people without a second thought? In the manga he's also seen drinking champagne with his guests, but that could be because of his status, the time period, and the overall culture back then.
- Alois as well. For the whole first episode, he goes from acting completely innocent to downright crazy within a few seconds, and switches back and forth between the two personas. Not to mention how he acts as if he is trying to seduce any male character within five feet of him.
Hansel and Gretel from Black Lagoon. The sheer number of people they kill (and how they do it) is just the start of how messed up these two are. And tragically, they can't even imagine the world any other way.
- Probably Revy. From what can be gathered from the tiny flashbacks, she was raised on the streets of a less-good place in New York City and probably learned her gun skills from gangsters, and killed someone using a pillow as a silencer when she was still pretty young.
Seta Soujirou of Rurouni Kenshin, given his horrible childhood and subsequent "adoption" by a Social Darwinist to act as his Dragon, slaughters people with a cheerful smile.
- Kenshin too, when he buried all the bodies of his guardians and the men who killed them, instead of, say, trying to find help.
In Saiyuki, there is a scene of a pre-teen Gojyo smoking in his room while his older brother calms his stepmother down.
Meet Maria Ushiromiya, 9-year-old walking encyclopedia of all things relating to Western occult lore and "black magic." Also has a rather irritating Evil Laugh and a habit of using it at incredibly inappropriate times, like after seeing her mother and 5 of her relatives' horribly mutilated corpses.
Essentially every child Contractor and Doll from Darker than Black qualifies for this. Lack of Empathy or becoming an Extreme Doormat will do that to you.
Japan Tengu Party Illustrated has a disturbing relationship between a Tengu man and the human child he kidnapped ostensibly to be the vessel for their leader (when he uses her to speak, he swallows her and uses her as his tongue). The child manages to escape the tengu, but the kidnapper is still concerned and obsessed with her. He eventually finds her phone number during a battle, but she never wants to see him again, and besides she's already safe in bed - with her teacher (she likes "magicians (the teacher) better then monsters (the tengu)") ^[1]
Vincent in Pandora Hearts. Taking scissors to stuffed toys? Indicative of problems, but not completely unheard of. Taking scissors to the eyes of Alice's cat? And what about ALICE HERSELF? That's not a good sign. It also borders on Psychopathic Manchild behavior since he still does it as a young adult.
- In confusing flashbacks and illustrations, Alice or more accurately, the Will of the Abyss... sometimes... also does this, displaying somewhat unsettlingly flirty behavior^{[dead link]} with Jack and being cheerfully vicious with Vincent. Eventually leading to yet more of this trope from Gilbert, who tries to strangle her.
Several characters in Now and Then, Here and There, especially Nabuca
This is a staple of Shōnen manga and sometimes Shoujo Demographic manga along with Harmful to Minors. It's usually treated lighthearted and without any real damage though, unless it's a plot device or a Deconstruction.
The first time we see Akane Awakusu in Durarara!!, she's gleefully chasing down Shizuo with a heavily modified stun gun and shouting "Die!" It turns out that this isn't exactly normal for her, as she was a Cheerful Child before she ran away from home and only did it because Izaya told her that Shizuo was an assassin who would kill her family.
The main cast of Higurashi no Naku Koro ni are well-known for their (usually) Hate Plague induced paranoia and murder sprees, among many other troubling behaviors. The four oldest characters are only about sixteen, with the youngest being somewhere between nine and twelve.
Seeing how it's a story about Child Soldiers, it's no surprise that this trope shows up a lot in Gunslinger Girl.
..And lets not even START with Narutaru.
In Project ARMS, there are quite a few children who end up this way, mostly because the Egrigori are very into using them for evil and dangerous experiments. The first ones we see are Al and Jeff Bowen, who attempt to blow up a high school partly for their mission, but moreso because they themselves were teased in school. Al spends the rest of the series methodically working his way through various battles and trying to kill a Keith with a gun at one point. Also, a flashback shows us that the twins murdered their own parents and killed a bunch of kids at their school with a poisonous gas that they invented to leave no traces. Then we get Carol, an adorable little girl who is introduced cheerfully telling Ryo that she has the power to twist and crush things like metal and human bones with her mind and that she very much enjoys the power that comes with doing this. It's implied that she only went through life by having people fear her, and Ryo calls her bluff on her enjoying it. Finally, we get Dark Alice, who is furious at the world for causing her death and is willing to nuke the entire planet to get her revenge.
Broly in the eighth Dragon Ball Z movie was shown in a flashback to destroy a planet, and then laugh hysterically as his father attempts to restrain him, all while he's a child. It's implied that this behavior stemmed from the trauma he endured on the day of his birth (Kakarot [Goku] crying next to him, his narrowly surviving execution by King Vegeta simply because the latter feared Broly's abnormal power level [he was born with a power level of 10,000], and later narrowly escaping Frieza's destruction of Planet Vegeta with his father.
- Broly is an extreme case, but Saiya-jin children in general are pretty disturbing by human standards. Originally, Kakarot was sent to Earth to wipe out all life forms. They may look cute and innocent, but looking is as far as it gets.
Played for laughs with Shin Chan, a preschool age boy with the libido of a middle-aged man, who constantly hits on hot women. His baby sister Hima is also occasionally shown to find grown men attractive.
It's downright creepy what children do in Naruto, even moreso that nobody seems to care that the main basis of the story is using children as Child Soldiers at the ripe old age of 12 until one of them goes half mad like Zabuza who murders the entire graduating class of his school BEFORE he was even old enough to enroll.
- In the beginning Naruto himself is especially fond of doing inappropriate things like sneaking into girl's bathing rooms and turning himself into a naked blond girl for laughs.

Comic Books

Damian Wayne in Grant Morrison's Batman. He's a ten-year-old who is firmly convinced that he's the natural successor to his father's legacy and Dick Grayson is an idiot. In addition to being a particularly grim (and potentially deadly) Robin, he is frighteningly efficient at running Wayne Enterprises.
- With Damian, several characters acknowledged it was a bad thing. Bruce originally didn't let him out in the field, and he only became Robin under Dick. Dick got him to act a little more normal though Dick's extreme own personal combo of experience, patience, and just being a good person. Stephanie, after learning Damian had never really played in his life, pretty much forced him onto a moon-bounce with her (though she admitted she was pretty sure he wasn't joking about stabbing her several times during her run) and usually ignored him when he got bratty. Damian acted a little more like a kid around Colin Wilkes (probably to put Colin, who was the same age, more at ease), but it was a major change form his original characterization.
- Tim and many other people still found him very unnerving even by the time of the reboot, though.
- Minor Batman villain "The General" was a boy-prodigy that was obsessed with military tactics, and used them to gain a foothold in Gotham's criminal world. That place has the worst luck, doesn't it?
- Well-Intentioned Extremist Anti-Hero Anarky is an intelligent, politically-aware would-be terrorist whose tactics against the corporate elite and the gears of the state range from "hacktivism" to straight-up bombing. He started doing all this when he was twelve.
If you are in any way associated with organized crime, Hit-Girl will brutally chop you up and shoot you in the head while cursing like a sailor. She's a cute 10 year old.
- A short scene in the film inverts this for a while.. Her father is very disturbed that she is acting like a normal girl, until she reveals she's screwing with him.
Crossed children appear to be no less foul-mouthed, kill-happy, or rape-happy than their adult counterparts.
The latest version of the Hellfire Club in X-Men. Members include a boy who sold his seven brothers into intergalactic slavery to claim the family fortune and another who dissected his first Atlantean when he was eight. The leader is a Self-Made Orphan.

Film

Rhoda Penmark in The Bad Seed is a multiple murderess before hitting puberty...and completely calm about the whole thing. They changed the ending for the film, though...
In Paper Moon, little Addie Pray is a full-fledged con artist who's partners with a man who may or may not be her real father. They stay together in hotels, in the same room.
Hailee Steinfeld's portrayal of the 14-year-old Mattie Ross in the Coen brothers' version of True Grit is, even though she isn't a child any more, very disconcerting in its seriousness and vengefulness.
The controversial Hounddog has Lewellen, its 11-year-old main character, drinking alcohol. This is considered normal in her family.
Lilya 4-ever has its title character drinking, smoking and sniffing glue at the age of 14. Then family troubles (specifically lack of any family) force her to enter prostitution. It all goes downhill from there.
The movie Young Thugs: Nostalgia has protagonist 6th grader Riichi Nakaba get drunk twice in the movie. In one scene his family and the guests at the party encourage him to get drunk.
The movie Sugar Cane Alley has eleven-year-old José Hassan and his friends (one a girl who is probably no older than eight bought the vodka and said it was for her parents to the clerk) get so drunk that they laugh as they set a shack on fire.
The sex worker Iris in Taxi Driver gives off an aura of grace, poise, and sexually-charged sophistication. She's also twelve. Jodie Foster's performance was by far the most unsettling thing about the film, even overshadowing de Niro.
Hard Candy runs on this alarmingly. The protagonist tracks downs, incapacitates, tortures, and drives to suicide a pedophile. She's a teenager.
In the 2005 adaptation of Tom Brown's Schooldays, Dr. Arnold is shocked that the students, some as young as ten or eleven, gamble, distill liquor, and keep guns.
Home Movie has this trope up to 11.
This is what makes The Innocents still terrifying even to a modern audience.
Kids is almost entirely made of this + Refuge in Audacity.
In City of God Lil Dice goes on a shooting spree in a hotel. Also, many children are involved in the gang war. (Horrifyingly enough, this is more or less Truth in Television.)
In Sweeney Todd: The Demon Barber of Fleet Street, the title character finds Toby easy to bribe with gin. As Toby tells Mrs. Lovett, they used to give the stuff to kids like him in the workhouse (child labor laws didn't exist way back when) so they could sleep—though as he mentions, you wouldn't ever want to sleep there, "not with the things that happen in the dark."
- Don't forget the ending, when he coldly and quietly slits Sweeney's throat.
Lawn Dogs has a lot of this. Not to mention some in the form of Corruption by a Minor, as Devon manages to convince her adult friend to steal chickens from a barn, and later, moon her father. And no, Devon is not portrayed as wise beyond her years either. She otherwise acts like a normal preteen girl, who happens to do some messed up stuff, in a realistically childish way.

"Also, children are expected to be a certain way, and I like the unexpectedness of how children really are if you watch them. (...) Sometimes children just don't go by the rules, they often have a natural inclination not to, which we as adults have often lost." - Naomi Wallace, screenwriter for Lawn Dogs

In The Good Son, 12 year old Henry (played by Macaulay Culkin) smokes, drinks alcohol, vandalizes property, builds homemade weapons, conducts horrible schemes, tortures and kills animals, and kills people all like it's an everyday thing.
Léon: The Professional starts with 12 year-old Mathilda (Natalie Portman) smoking and hitting on the middle-aged neighbor. This is all before she becomes an assassin's apprentice.
Blood Diamond had Child Soldiers swaggering around and swearing profusely in Engrish, which was funny until they started to shoot at Leonardo DiCaprio.
Speaking of Leonardo DiCaprio, he himself had portrayed a 14-year-old Catholic school boy's descent into heroin-addiction and prostitution in order to support his drug habit in 1995's The Basketball Diaries.
Total Eclipse, another Leonardo DiCaprio movie (boy, he surely went through a phase of acting in edgy, indie roles in 1995...). He plays Arthur Rimbaud, a wild and bratty teenager who gets into a sexual relationship with an older, married man. The entire movie highlights how sick and twisted their relationship is.
Let's not forget scamming, scheming, stealing, swearing, smoking little Addie in Paper Moon.
In RoboCop 2 there's Hob, the villain's main henchman, who is a boy of about 12 and very competent too.
- One scene features a Little League baseball team (including their coach) robbing a sporting goods store.
Tideland consists entirely of this, although Jeliza-Rosa does not fully realize everything that's going on around her and keeps acting and (probably) thinking like a child while she does stuff like preparing the syringe for her drug-addict father and seducing a grown man. (Thankfully, he's mentally about the same age, but it's still very, very disturbing.)
The Heart Is Deceitful Above All Things has the protagonist drinking alcohol at the age of seven and seducing Marilyn Manson at the age of eleven. Among other things.
Mindy/Hit-Girl of Kick-Ass cusses like a sailor (from random F-Bombs to her introductory quote: "Ok you cunts, let's see what you can do now"). [ Oh, and she's a trained killer who can drop a room full of other trained killers with just a couple of handguns. Her actress did all of her own stunts including the Butterfly Knife display.
Trish from Angels Revenge, though it might be Justified Trope since she's a young teenager. She gets just a little too excited at a drug dealer's unwanted bris, she latches onto another drug dealer's car in order to track him, and she fatally shoots a kingpin at the end of the movie.
Pretty much the entire cast of kids in Twelve And Holding.
River Tam in Serenity. Better than 50% of the on-screen kills are hers. She's a teenager.

Literature

The very controversial The Bad Seed portrayed a pre-teen girl who's a multiple murderess.
Addie Pray, the novel on which the Paper Moon movie and TV series were based, is narrated by a pre-teen girl who's a full-fledged swindler learning from an established con man.
Duumvirate lives and breathes this trope. Even the littlest kids are perfectly willing to kill at the drop of a hat. It's all just a game to them.
Rather freakily lampshaded in Brave New World, where the childhood conditioning all the citizens are exposed to encourages children to act sexually towards each other at about pre-school age. The people administering said conditioning laugh about how those poor unenlightened souls way back when would have treated such behavior as disturbing.
At the age of twelve, Lolita seduces her stepfather. He's not her first lover. (Or at least that's what daddy wants us to think.)
- It quickly becomes obvious that while she fooled around a bit at summer camp, she's not really prepared for what she's getting into when she gives a grown (and rather disturbed) man the opportunity he's been waiting for.
Gone (novel), by Michael Grant, has this in spades. The entire cast is aged fifteen and under, and Sam and Lana both dwell on how disturbing it is to see young children drinking, smoking, and doing drugs. Not to mention the plentiful violence.
The Redwall series. Oh, Dark Forest Gates, the Redwall series. The titular first installment features a season-and-a-half year old squirrel—described in the text as a baby and not talking yet—who is personally responsible for the horrible deaths of at least ten vermin, and assists in the killing of many others by rolling a hedgehog over them in the middle of a battlefield. He's also given a sharp dagger by a hare who thinks nothing unusual of a kid stabbing people with one hand and sucking the other. By comparison, the young, gangly teenager that goes on to see new friends and an adoptive father/Abbot poisoned to death, kills massive numbers of vermin, faces and decapitates a snake that could eat him alive, and comes plummeting from the top of an Abbey with a bird stuck in his shoulder, all by the age of thirteen seasons, seems almost reasonable. Oh, and gets married and has a son before he's sixteen seasons. Combines with Angst? What Angst?. This may have been intentional Values Dissonance, as the series is set in pseudo-10th century England WITH FURRIES, but has been somewhat dialed down in the sequels... which still include the slavery of preteen children and the murder of their slavers.
In the Green-Sky Trilogy, Pomma's addiction to wissenberries.
The Alienist has multiple characters all over the novel.^{[please verify]}
The Tomorrow Series: Aside from the fact that the viewpoint characters are only 16 – 17 years old, and essentially learning to become guerrilla fighters as the series progresses, the group of kids living in Stratton are a more depressing version of the trope: by The Night Is For Hunting, when the main characters meet them, they are well-accustomed to gunfights and mugging people in alleyways.
The Dresden Files has the Archive: when warns you that she will kill you if you challenge her authority or otherwise threaten her, you'd better believe it. Her bodyguard thinks it's creepier when she actually does act her age though.
Artemis Fowl
Ender Wiggin, at six, beats a bully to death, because he knows that being merciless will lead him to victory. Granted, his intention wasn't to kill the bully - just beat him so badly that he and the other bullies would be terrified of Ender from then on, and thus leave him alone.
- Somewhat justified in that the school he attends deliberately recruits children who act and think "older" than their age in order to train them to be part of the war machine.
Tom Riddle from Harry Potter was an ultimately creepy kid. As a child, he tormented his fellow orphans - even murdering one's pet rabbit. When he went to Hogwarts he learned to be sly and manipulative, continuing his evil acts and a couple of murders without being suspected by the older, more powerful wizards who could pose a threat. Then, of course, he became Lord Voldemort.
Arya Stark from A Song of Ice and Fire committed her first premeditated murder at age ten. It wasn't her first kill, just the first one she planned out deliberately. Oh, and she's one of the heroic characters.
In The Iron King, Meghan is shocked to hear her four-year-old half-brother tell her best friend "Go fuck yourself!" Justified in that the kid is actually a changeling. Her real half-brother is a perfectly normal, sweet kid.
Daine in Tamora Pierce's Immortals series hunts down and slaughters the bandits who killed her family, aged twelve. Justified by her grief and the fact that her gift was making her think she was a wolf, but made more unsettling by the fact that, when she does eventually tell her friends about it, most of them simply shrug it off. On the other hand, this takes place in a world where knighthood training starts at the age of 10 and it's loosely based on medieval times where kids grew up faster. And her friends have gone through some fairly dark stuff themselves...
The main plot point of The Hunger Games - teens and preteens as young as twelve forced into an arena to fight each other to the death. And some of them are disturbingly good at it.
The Phantom of the Opera mentions "the Little Sultana" who enjoyed torturing people with the Phantom's wonderful devices.
In The Coldest Winter Ever by Sister Souljah, Winter, the 16 year old daughter of a drug dealer, engages in lots of adult behaviors. For example, she offhandedly mentions that she lost her virginity at age 12, which was "kind of late". The novel ends with her getting 15 years in prison for possession of illegal drugs.
Mormon in The Book of Mormon begins leading the entire Nephite army at the age of 15.
Robert Westall's The Machine Gunners presents some examples of this. The plot of the book involves a group of wartime children between 11 and 16 who steal a working machine gun from a crashed plane, hide it from the authorities, construct a bunker and emplacement for it; hiding two of their number from the adults and later a captured German airman in said bunker and open fire on a group of Polish soldiers during what everyone thinks is a Nazi invasion.
Although Asher and Otto are the worst offenders, Someone Else's War is full of this. Which is only natural, because it's a story about Child Soldiers in the Lord's Resistance Army.
In Crooked House by Agatha Christie, twelve-year-old Josephine investigates the murder of her grandfather, using her naturally snoopy nature to provide clues that the outsiders to the family never manage to find. Then it turns out she's the murderer, having decided to kill her grandfather over his not getting her ballet lessons. She decides to investigate the murder to get further attention from her family and the police.
Stephen King's IT has The Losers Club defeat IT/Pennywise, but they remain lost in the sewers. Beverly tells the group that the only way out is to have a orgy as a way of "restoring their unity". Stephen King declared that he actually regretted ever writing it in, and it was thankfully left out of both adaptations.

Live-Action TV

In an episode of Sex and the City, Samantha is jealous of a very rich 13-year-old girl for whom she organizes a Bat Mitzvah party. When she overhears the 13-year-old telling her friends about giving blowjobs to keep a man, Sam interrupts to say that this is wrong. When the 13-year-old replies that she has been giving blowjobs since she was 12 and that she knows how the world works, Sam is released from her jealousy as she realizes that at least she had a childhood.
There's an episode of House where a mother brings her young daughter into the clinic for possible epileptic behavior. House examines the girl, and determines that she's merely been "ya-yaing the sisterhood". The mother is shocked, to say the least, but House says that it's reasonable behavior, if a bit atypical.
Jayne Cobb from Firefly. It's revealed that at ten years old Jayne was shooting spaceport varmints for the bounties, which is marginally acceptable even if ten is rather young to have unsupervised access to a .22 rifle... and using the money he earned to bet on gladiator blood sports and buy beer.
- River Goddamn Tam, most especially in Serenity, but she's hijacked spaceships and shot people (without looking, yet still perfectly accurate) by the end of the show. She's in her teens.
In one episode of Bones, the murderer turns out to be an 11-year-old girl, who shoots her tutor with a shotgun when he refuses to help her cheat on a school project.
CSI had one in the form of a 12 year old girl who was taking senior level high school courses. At her older brother's trial for murder of a classmate, she testifies that she's the real murderer and produces evidence to support her case. She pulls off the plan so well that she convinces the court that there is too much doubt to her brother's involvement (mainly, that he was a D student in chemistry and the murderer needed to know how to handle pure Sodium) and that there was too much doubt to convict her (she was too small to move the victim's body). As if that wasn't the worst of it, she says to Sarah that had she been convicted, she could get her degree by 18 and/or write a book about the crime, since Nevada has no "Son of Sam" law. Finally, it was revealed that she had no involvement in the murder and Sarah just got played.
- It's even worse in the continued episode later on, when it's revealed her Yandere fixation on her brother prompts her to murder his girlfriend and blame him for it. Her motivation is that it will get rid of any "obstacles between them" and that, by continuously visiting him while he's in prison, he'll fall in love with her.
Leverage: Poor Parker. Mostly, it's played for laughs, but the ages at which she started committing various crimes is alarming. Car stealing at twelve, and getaway driving before that. Cut to a flashback of what looks like a nine year old Parker skidding around an old lady with a terrified robber in the passenger seat.
In one episode of Greys Anatomy, a man is brought into the hospital after supposedly being accidentally shot by his six-year-old daughter, using a gun that had been carelessly left outside. However, scans show that this man has been shot 17 times. When the daughter is questioned about the event, she asks why her father wouldn't just die, since she had shot him so many times. As it turns out, the girl and her mother had been putting up with severe abuse at the hand of the alcoholic father. The girl, seeing her father begin another attack on his wife, grabbed the gun (which had been left in an easily accessible place) and shot her father.
Parodied in a Jam sketch where a man believes he has accidentally killed his friend during an argument. He calls a professional killer/"cleaner" named Maria to dispose of the body, but she turns out to be only six years old. She uses language that would make a sailor blush, carries a gun, and when the victim wakes up (revealing that he was only unconscious) she shoots him in the head then hacks him to bits with a saw blade. In the end, the police are called and Maria instantly reverts to a cutesy child act.
- Jam was based on the radio series Blue Jam, which featured several sketches about Maria. More disturbingly, in this version she is only four years old!
An episode of Criminal Minds focused on a series of murders of young children. They turned out to have been committed by a young boy (the son of their original suspect), who, in his own words, did it "because I wanted to."
Inverted in Game of Thrones; Robin Arryn is ten years old and still breastfeeding.
- Also played horrifyingly straight throughout the series.
Francis Wilkerson, or heck, any of the kids from Malcolm in the Middle, easily qualify. Francis, aside from attempting to douse his teddy bear (as noted in the subtrope "Kids trying this behavior out for the first time" below), also frequently tortured his younger brothers (barring Dewey), stole their toys, locked them in a closet, and scarred Reese with a bayonette, all as a child, and he also implies when telling Dewey this that this is exactly what being a good brother is all about. As a teen, he frequently goes on destructive rampages/rebellions, such as stealing his mother's car, sleeping around, smoking, drinking, getting four nose pierces, and other similar behaviors all just to spite his mother or just for the heck of it. Reese is very much prone to violence, and enjoys hurting people.
The Gallagher Children in Shameless are all examples of this (or were, at some point in the show's backstory), but they run the spectrum from Promoted to Parent "reponsible" types like Fiona and Debbie to absurdly worldly but irresponsible or immature Street Urchin-types like Lip and Carl (who is arguably way more naive than the others). Ian's somewhere in the middle, being self-disciplined and responsible but not taking an active role in raising his younger siblings.
A major theme in The Wire is that the children at the low-rises of Baltimore are already involved in the drug game by the age of ten, even earlier. On the violence aspect, Snoop and Kenard come to mind.

Music

In "Brenda's Got a Baby" by 2Pac, Brenda (then 12 years old) gets into a relationship with her 20-something cousin after becoming frustrated with life at home. She becomes pregnant, but manages to hide the pregnancy from her family. She ends up giving birth on the floor of the girls' bathroom at school, and tries to dispose of the baby in a dumpster (only to feel bad and take it out). She and her mother are constantly at each others' throats, and finally Brenda is kicked out of the house. She is too young to be hired for honest work and has no place to go, so she sells drugs...until she is robbed at gunpoint and is driven to prostitution. It does not end well.

Tabletop Games

Wicked witches in Witch Girls Adventures and the comics that spawned it are big on Evil Smoking. Children aren't an exception.
Blood Claws in Warhammer 40,000. Granted, they're not actually children (more along the lines of 18+ due to how long it takes to become a Space Marine), but they just came into adulthood and will blindly charge towards a 40' towering monstrosity while laughing their heads off, not exactly behaviour suited to the average teenager (especially since many older warriors would run away in fear from said monsters).

Theatre

The entirety of How I Learned to Drive.

Video Games

Sign on to any online shooter (preferably an Xbox 360 shooter Rated "M" for Money and/or Manly for maximum results) and prepare to be called a nigger, faggot, and just about any other offensive word you can think of by Internet Tough Guys 12 and under.
Mildly done in Psychonauts. The protagonist and his peers are all ten-year-olds, yet some of the kids have an odd fascination with hooking up and making out.
- Then there's Crystal and Clem. They're seen messing around with poison, and there's one scene where they talk about how everyone is "going to be sorry" in very somber monotones far divorced from their usual chirpy facade. It's never explicitly established what their end goal is, but a vague misunderstanding of what happened to Obi-Wan Kenobi seems to be involved.
Illyasviel von Einzbern is a... strange case. At first, she's trying to kill Shirou and Rin... then depending on the route she goes to play with Shirou, her "onii-chan", frequently. Then it turns out she's a homunculus created as a vessel for the Holy Grail. Finally it's revealed that she's 18.
- Plus she also tries to have sex with Shirou at two points in Fate and one in Heaven's Feel. Which is... a little disturbing.
Does it bother anyone else that Mission Vao, a fourteen-year-old twi'lek, can happily slaughter her way through hundreds of people when previously the worst thing she did was pick pockets and scam people?
Rule of Rose: Byzantine plotting, power struggles, and even torture are everyday occurrences in the Aristocrat Club of the Rose Garden Orphanage, and depending on the player's interpretation, some of them don't even shy away from murder if they can get away with it. And manipulating a serial killer to commit murders is definite canon for one of the characters, although that wasn't considered typical behaviour even for her.
The imagery of mock suicide by teenagers (and, in one case, an elementary-school kid) in Persona 3 is more than a little disturbing, and likely the primary reason for the game's "M" rating in North America.
Borderlands 2 introduces Tiny Tina, a 13-year-old girl who has a psychotic personality, and even displays interest in two adult women, Maya and Mad Moxxi. Her hobbies include having tea parties, role-playing, and exploding Bandits while singing:

"All around the Sta-actus plant, the stalker chased the bandit, the stalker thought 'twas all in fun - POP! (Bandit explodes) Goes the bandit!"

In the game Kindergarten, the students almost act like adults. Examples such as: Bugs will kill you if the player doesn't give him half his money, Cindy knowing the word "rape" and play house too literally, and Monty acting like a drug-dealer because he has both cigarettes and the Principal's pills.

Web Comics

Chelsie Warner, the Creepy Child of Concession. She suffers from gender dysphoria, and was born "Charles" until her parents allowed her to start dressing and living as a girl. This itself isn't what's troubling, otherwise we'd be dealing with Unfortunate Implications, but she displays violent tendencies in her very first appearance by stabbing Artie in the eye with a crayon. She then rapes him when he's too delirious to know what's going on. It was later revealed that her hypersexual behaviour was related to a form of bipolar disorder, and she joined a harem of preteen boys run by the practicing paedophile Kate, who specifically seeks out children with this disorder because she believes that allowing them to give in to urges which are already there doesn't count as abuse. The author points out that he knows that it does count, but Kate does not know that or refuses to believe it. Luckily, the Where Are They Now? Epilogue shows that by the time Chelsie's an adult she's transitioned fully to female and is much more mentally stable under the care of her adopted father, the local priest Father Tim.
Namah in Dreamkeepers Prelude is a milder version then people on this page, but she still did a Slasher Smile when she went into the ventilation system, stole knives, poured hot sauce in the eyes of one of her guards. Considering that she is being kept in her room to prevent knowledge of a secret affair being leaked, it's kinda justified.
Samantha Wight of Suppression has a habit of lecturing people about the futility of everything and, at best, is only mildly annoyed at being stabbed through the heart.
Nadia (and possibly Dark) in Kagerou, although whether they're actually children, or even real, is highly debatable. Their actions are made more disturbing by the presence of Kid, who is very childlike.
The trolls of Homestuck do not, as a rule, have much in the way of childhoods - but some of them develop a strong interest in collectible card games or rainbow drinker romance novels, and others begin earnestly studying for a career in law enforcement or become mass murderers by the age of thirteen.
- There's also Alpha Mom. Like her Beta counterpart, she's a Bottle Fairy. Unlike her Beta counterpart, she's only fifteen. Of course, she's one of the last two humans on the planet, and was raised by childlike Chess people.

Web Original

There Will Be Brawl has Ness and Lucas, who bad enough to make all of the other supposed Big Badss nervous.
In Mall Fight, Sakura acts like she is at least sixteen, despite only being nine, and often has sex with her actually teenage boyfriend. The only time she really acted her age was when she was aged down to five a little before the latest reboot.

Western Animation

The Delightful Children From Down The Lane from Codename: Kids Next Door.
When we see Azula in a flashback to when she was about 8 years old she engages in typical activities such as teasing her brother and her friend who has a crush on him, doing cartwheels, throwing rocks at animals, throwing fireballs at people, hopefully suggesting that her uncle and cousin might die in battle so her father can inherit the throne, setting dolls on fire, mocking her uncle for leaving a battle after her cousin died, cheerfully telling her brother and mother that her father has been ordered to murder her brother...

Ursa: What is wrong with that child?

Played for laughs in South Park, where pretty much all the kids (except Butters) curse and do other adult behavior all the time. Taken to extremes with Cartman, however, who has gone so far as attempting to start new Holocausts.
On Daria, Brittany's little brother Brian not only acts out of control, he is apparently the reason why the family doesn't even bother naming their pets anymore.
As a kid, Big Bad Wannabe Evil Genius Jack Spicer asked for knife-throwing lessons. His mom sent him figure skating. So he made a robot out of her juicer. As a Teen Genius, he's trying to Take Over the World with a robot army... with winter sports as a surprise skill.

Real Life

Comedian Brendon Burns tells a story about catching his 5 year old son masturbating with a soaped up shark toy, his advice was:

Burns: DON'T DO THAT!
Son: Why not?
Burns: Because adults don't like it when little kids do that, and I wasn't allowed to do it when I was your age and..... y'know what, go ahead, just don't do it at school.
Son: Why not?
Burns: See rule #1. (Rule 1 is "it'll suck, and you'll hate me for letting you do it")

Played for laughs: Catholic speaker Chris Padgett tells a story of when his young son first learned a bad word- "boobie"- and would not stop saying it. Eventually, Chris's older daughter sits down to talk to him:

Daughter: You can't say that word anymore, it's bad.
Son: Yes I can, boobie.
Daughter: Jesus wouldn't want you to say that word, right?
Son: Yes I would.
Padgett: Great, my kid thinks he's Jesus.

Chain smoking guerrilla leaders the Htoo Twins. They also claimed to be bulletproof and have armies of invisible soldiers.
2 year old smokes 40 cigarettes a day.
It's actually very common for babies and toddlers to masturbate. It's just pleasure to them though.
- Fetuses have been observed doing just that on ultrasound.
Kevin Smith, on one of the "An Evening With Kevin Smith"s, describes his daughter learning her first naughty word (bullshit) while she was a toddler. Unlike most examples of this trope, this was intensely hilarious to Smith and his wife, who egged her on; she even got creative with it (dogshit, mommyshit, daddyshit). Then they said, "Do you know what 'shit' means?" "No." They told her, and the girl got very quiet...
Spotted hyena cubs, the second they've exited the womb, tend to fight each other to the death, especially if they're the same sex. They've also been seen to try to "mock-mate" with each other. Yikes.

Trying for the First Time

Anime and Manga

One Piece showed Sanji started his smoking habit at age nine trying to be more adult.
A little later, but in Ichigo Mashimaro, Nobue started trying to smoke in middle school. It nauseated her when she first tried it, but she "powered through" until it didn't make her sick anymore, and now she's addicted. What started it all, however, is when a smoker left a pack behind on a park bench when Nobue was 11. Curious, she picked it up and looked at it. The warning label scared her off of starting for a while, although she did start holding a cigarette in her hand in an attempt to look cool.

Comic Books

In Belgian comic Violine, the titular 10-year-old drinks whiskey and gets clearly drunk off it, when it's given to her as part of a celebration held by friendly natives in an African country.

Film

Again in Hounddog, Lewellen is tricked into doing a naked dance for a much older man for Elvis tickets and gets raped because of it. This carried over into Real Life, where many people were shocked that 12-year-old Dakota Fanning had played such a scene herself.
O-Ren Ishii of Kill Bill commits her first murder at the age of eleven, an incredibly bloody revenge upon Boss Matsumoto, who just two years earlier murdered both of her parents with the help of his men. And the reason that O-Ren was able to get close enough to Matsumoto to kill him? Matsumoto was a pedophile.

Jokes

A mailman is making his rounds, but one of his deliveries is a package that requires a signature. So he goes up to the house, knocks on the door, and a 12-year-old kid with a cigarette in one hand and a glass of scotch in the other answers it:

Mailman: Uh... hi. Are your parents home?
The kid takes a puff from the cigarette
Kid: What the fuck do you think?