ThreadsPerChild:
This directive sets the number of threads created by each child process (1 for Windows).
The child creates these threads at startup and never creates more.
ThreadsPerChild 256 (default is 64)

MaxRequestsPerChild:
Limit on the number of requests that an individual child server will handle during its life.
MaxRequestsPerChild 0 (This is the default value on Windows)

Setting MaxRequestsPerChild to a non-zero limit has two beneficial effects:
* it limits the amount of memory that process can consume by (accidental) memory leakage;
* by giving processes a finite lifetime, it helps reduce the number of processes when the server load reduces.

Note:
ThreadsPerChild Directive scope: server config
MaxRequestsPerChild Directive scope: server config

http://httpd.apache.org/docs/2.2/mod/mpm_common.html#ThreadsPerChild
http://httpd.apache.org/docs/2.2/mod/mpm_common.html#MaxRequestsPerChild