This seems like a very simple question. I'm looking for something like sub-page.php or page-child.php where I can do some different things on the child pages of my theme.
They are different enough in design and content that I'm having to use a lot of php or the CSS .page-child class to do all the dirty work. I'm looking for a simpler method.
One caveat - I would like this to happen automatically so I don't have to tell the client "make sure to always select the 'subpage' template when you create a subpage!" which is precarious..