I think you will all enjoy 'Ohana. We stayed at Poly last fall and took Monorail to Contemporary for California Grille, so you will have no trouble with transportation.
The meal is fixed price and all inclusive (alcohol and special desserts are extra--we didn't need either). They start you off with a lazy susan for the table filled with seafood wontons, salad, rice, vegetables and wings, plus dipping sauces--all you can eat. Then they bring huge skewers of grilled turkey, pork, beef and shrimp and serve as much as you want. Dessert is pineapple with warm caramel dipping sauce.
This is a great restaurant for anyone, but especially kids who enjoy the games. Views are of the water and MK. Make sure to stroll around the grounds before or after dinner--just beautiful with the torches lit.
Since you are so close, you might want to try the Poly's Kona Cafe for breakfast. Excellent coffee.
Aloha, and have a wonderful time!