You'll get more and better assistance if you take the time to explain in more detail what you are trying to achieve and why. And what plaform you are running on.

To kill a parent and all its children on Unix, you can make the parent a process group leader via the Perl builtin setpgrp function or the POSIX module. With that done, any children this process creates will also be a member of this process group, so sending a signal to this process group will kill the parent and all its children and their children and so on.

On Windows, which does not support process groups, you can achieve the same thing via Win32 Jobs, accessible from Perl via the Win32::Job module.