Childrens parties are not the time to worry about nutrition. If he wants a bouncy castle and a play station you can't go far wrong. Yes..they will fling themselves around like loons but on a bouncy castle should be well directed...ditto play station...serve hot dogs and coke and chocolate cake. Enjoy...they will
I wouldn't have a problem with my 10.7 yo DD1 being offered Coke or lemonade at a birthday bash. It's a treat for her. Mind you I would hope for plenty of water or dilute juice on offer to counteract the thirst from all that bouncing!