Thanks for the assist Era.
All that can be returned from a child is it's pid without ipc.
That's all my example does. Remember that at fork the parents address space is copied into the child. Afterwards no assignments are shared.
The exception is vfork. There are some ugly hacks that can accomplish what you need using this. You may want to consider threads instead. It sounds like what you have in mind.

Traditionally in a process (ipc) paradigm: Pipes are simple and clean.
Everything else is going to take time to get used to.