1. Do you have the patience to coach 5 year old kids? I know I don't.
2. Are you the kind of guy who can just shut up and do what you're told? I know I can't.
For me, the decision would be simple - forget the 5 year old team. As for the AC job - you should give some thought to your own limitations. I have a hard time minding my own business. That means I either have to be on a staff that has a clue, or have enough authority to make changes and be heard.
Me in your shoes - I have a chat with the inexperienced HC. And I describe that situation last year, and flat out tell him you will respect his authority, but you have zero patience for willful cluelessness. If you're kicking his ass with 7 stiffs, then your expectation would be that he's going to come to you and ask what he needs to do to stop getting his ass kicked, not hamstring you to cover up his own foolishness. Be a prick up front, then at least he can make a decision based on worst case scenario with you.