What you can do is only have the parent take out the children. The parent process forks off the children, and then wait()'s until one of the children die's. Then it kills all of its children. One advantage is that the parent can keep track of the children pid's and doesn't need to kill the process group.

If you need to have the parent do some processing, the parent could do the killing in a SIG{CHLD} handler. You would need to worry about race conditions since the killed children will produce CHLD signals.

BTW, I think your code doesn't work because kill() sends the signal to process group when the signal is negative, not the process id. The documentation says that negative process numbers only work on SysV-based systems.