The only DAK location I haven't eaten at is Restaurantosaurus, and while every restaurant in DAK is quick-service, Restaurantosaurus is the only one that serves burgers-and-chicken nuggets style fast-food. Flame Tree BBQ offers a variety of smoked meats, fries, onion rings, etc, Pizzafari is mainly individual pizzas, caesar salads, a deli sandwich, and a pasta dish, and Tusker House is rotisserie chicken, salmon, etc.
Of the three, Pizzafari tends to have the smallest portions, and I would go with Tusker House or Flame Tree (Tusker House has a bakery as well, which might tip the scales.) Either way, when you visit DAK with teenagers, you should definitely consider the Meal+ certificates. $12 gets you an entree & large drink, box of popcorn or ice cream, and a bottled soda or bottled water (three-part perforated voucher you can use as you wish throughout the day).
Have fun!