I think you're going to want more than a single scalar. A hash or an array would be a better fit. You at best have a one-to-many relationship here of one parent and many children. At worst you have a tree of processes with children, grandchildren, etc.

The really bad part is there's no way for us to reason about what that structure is without seeing the loop.

There's a thread on Usenet (well, archived on Google Groups actually) I'd recommend. Fork lots of children as well as merlyn's articles listed there ( Forking Parallel Link Checker and Getting Your Kids To Do The Work).

One thing to remember is you have data in the parent about the children and data in the children about the parent, but you don't have any trustworthy data about the children in the other children. Another is that you don't automatically have a good way to communicate among the processes just because they are related.