Fork() execution and number of processes
Each fork call duplicate process, so after first call there are two of them. You may call the one with pid = 0, the master process (parent, top, original).

After that two processes are in the second line (second fork), executing it, there are four processes now. I have not seen such distinction, but you may at that point say that two of them are child processes.

After the final fork, there are eight processes altogether, according to your materials, the original process is called parent and the rest are childs.

To draw it properly you should create a tree, with two children after each fork, where in fact one of them is the original caller.