WampServer

last night my wamp server was down and i found this in apach_error.log:

[Wed Jul 11 03:15:38 2012] [warn] Server ran out of threads to serve requests. Consider raising the ThreadsPerChild setting
[Wed Jul 11 10:44:17 2012] [notice] Parent: Received shutdown signal -- Shutting down the server.
[Wed Jul 11 10:44:17 2012] [notice] Child 2480: Exit event signaled. Child process is ending.
[Wed Jul 11 10:44:18 2012] [notice] Child 2480: Released the start mutex
[Wed Jul 11 10:44:47 2012] [notice] Parent: Forcing termination of child process 404
.........

I think this was caused by too busy visit and I need to increase the value of Threadsperchild, I wonder if I need to add such statements in the httpd.conf:

<IfModule .......>
ThreadsPerChild 512
MaxRequestsPerChild 0
</IfModule>

but I am not sure which module to modify or shoud I modify another setting file? like httpd-mpm.conf instead of httpd.conf?

any help, please!