Creating a child record from a button on the parent form and automatically return back to the parent form after the child has been saved.

When you put th Report Link field type for the ROot Cases in the Damanage Parts form, you can specify that the child records ( just one record in your case) should appear directly on the form in a report. You may them create an unfiltered report to use to decide which columns (fields) of the rooot causes, you want to show to the users.

Users can then choose to either view the root because or edit it.