If you're not using something like Parallel::ForkManager then you should be using wait or waitpid to wait for your child processes. You should also investigate $SIG{'CHLD'} and determine what you want for that. If you're writing from one to the other, also consider $SIG{'PIPE'}.

If you haven't, read up on perlipc (or perldoc perlipc or man perlipc) to learn some other stuff. Also, I can definitely recommend APUE and Unix Network Programming, Volume 2: Interprocess Communication. Advanced Unix Programming by Rochkind, The Unix Programming Environment by Kernighan and Pike, and lots of other material exist that could help, too.