The examples online aren't working for me. I've tried it two ways thus far.
Currently - I have a "main process" that has a Message Throw followed directly by a Message Catch. The Message Throw calls a child process with a "start process" event. That child process concludes with a "message throw" which is a process call to the parent message catch, followed by an end event.
Here are some pictures to help illustrate:
Child: Start - https://i.imgur.com/pEGKeUz.png
Child: End - https://i.imgur.com/oT612P3.png