Anything's possible, but I think you may want to have a plan together before you start working out this type of set up. Do you have any idea of what your set up is going to be? I also have another question why would you want this again? I mean think about it you'll be trying to listen to the GPS and the kids will be listening to music. It's not like you're in seperate rooms or that they'll have headphones.
Anyways a simple unexplained answer to your question is yeah you can do it. You'd have to have an a/v switch in between your two inputs and your amp or hu.