ProofHub allows you that you can see the dependent tasks in a task detail view. Once you have opened a task and checked off the Task dependency option then you should be able to view the predecessor (parent task) and successor (child task) all in one place.
If you want to open the predecessor or successor task details, you can click on this icon, and the Predecessor and successor view will open.
Predecessor and successor task view in ProofHub
Whenever the task gets completed, the subscribers on the following task will get an email notification that Successor task has been completed so that they can start the following tasks.