{
   local $SIG{CHLD} = 'IGNORE';

   ... launch child ...

   if (sleep(20)) {
      kill(KILL => $child_pid);

      # Wait for child to die before restoring $SIG{CHLD}.
      # Unlikely race condition.
      while (kill(0, $child_pid)) {
         sleep(1) or last;
      }
   }
}