Symptoms

IPC event only shows processes in the current project.
 

Diagnoses

The IPC event browse button lists all the Process in the current solution, not all those deployed on the server. The reason for this is, during design time, context is required to the child process. E.g if you want to send data from parent process to child process or vice versa via data fields.
 

Resolution

You can easily add an existing project to your current one by opening your parent process. Right click on your project, then click 'Add' --> 'Existing Project Item'. Select your "child" workflow.

Go back to your IPC wizard and click on the browse button. You’ll notice that now your child process is listed there.