prefork doesn't appear to be listening to MaxClients in config file

Question

Apologies in advance if this is a stupid question, I'm new to all of this!

I have prefork installed on a ubuntu server which I confirmed by running

aptitude search apache2-mpm-

Which gave me

p   apache2-mpm-event                                                                                              - Apache HTTP Server - event driven model
p   apache2-mpm-itk                                                                                                - multiuser MPM for Apache 2.2
i A apache2-mpm-prefork                                                                                            - Apache HTTP Server - traditional non-threaded model
p   apache2-mpm-worker                                                                                             - Apache HTTP Server - high speed threaded model
root@redflagwiki:/etc/apache2/sites-enabled# vi /etc/apache2/apache2.conf
root@redflagwiki:/etc/apache2/sites-enabled# aptitude search apache2-mpm-
p   apache2-mpm-event                                                                                              - Apache HTTP Server - event driven model
p   apache2-mpm-itk                                                                                                - multiuser MPM for Apache 2.2
i A apache2-mpm-prefork                                                                                            - Apache HTTP Server - traditional non-threaded model
p   apache2-mpm-worker                                                                                             - Apache HTTP Server - high speed threaded model

In my apache2.conf file I have

<IfModule mpm_prefork_module>
    StartServers          5
    MinSpareServers       5
    MaxSpareServers      10
    MaxClients          100
    MaxRequestsPerChild   0
</IfModule>

but this seems to being ignored as the server is allowing apache to run 200+ times until it dies and then has to be restarted.

Any ideas?