In your code, if the ps command returns the processes in different order, you might duplicate or miss childs. Do a sort { $a <=> $b } ... to insure that the array is in a consistent order after different calls.

Note that if a child terminates between calls to FETCH, you're bound to miss / loss childs while traversing the array.

Perhaps a better way to approach this problem would be catching SIG_CHLD and providing a custom fork() method that kept track of how many children and when they die. This would avoid doing a ps for each element of the array, each time you iterate over it.

Finally, if you're on a multiuser system, please place a sleep(1) or something like that in the infinite loop of the child. You're burning CPU time for every children you spawn in your test.

Good luck and hope this helps...