I'm actually starting the child processes with fork(), not system(), and I do check to make sure the fork was successful. If the child exited right away, I might agree that this could be the explanation, but the problem child lives for just as long as all the others. (The script prints out "1 child running" ... "20 children running" ... time passes while children do work ... "19 children running" "18 children running" ... "0 children running", then exits). There is every indication that the child process does all the work it's supposed to, and no indication that it actually exits abnormally in any way.