The problem is that your buffers are filling up. You keep on writing to your pipe, but you don't read from it until all children have finished writing. But eventually, the buffer fills up, the child that's currently writing cannot write and hence will block. In the main time, your main program is waiting for the child to exit.

So, you have a deadlock. You have a child that is waiting for the parent to read something, and a parent that's waiting for a child to terminate.

Abigail