I can't think of a restaurant on property where you would necessarily pay for a 3 year old to eat from your meal. Obviously, quick service doesn't charge by the head -- you would just pay for what you order. For table service where you pay for what you order, again, you just pay for what you order. For table service that charges by the head USUALLY 3 and under are considered guests of Mickey. Usually these are buffet or family style where the 3yo could eat whatever they want. The one exception I can think of are dining packages where you pay a price per head, but it's not buffet/family style (for instance, the Fantasmic dining package). In that case, the CM will usually say that the 3yo can either eat off your plate, or you can pay the child price for them.