The first question that comes to mind is, why on earth would you need to run a dhcpclient script a 1000 times simultaneously? Are you setting up a thousand virtual interfaces on your machine and need to assign them an address instantly?

That being said, if your children do not need to share state use fork, if they do, investigate whether one of the IPC methods available are sufficient for your needs. If they're not, use threads. (This goes for *NIX, Windows apparently has its own issues with fork(), though I'm not knowledgeable enough about them to really comment).

For examples see the documentation for perlipc and threads.