Again to confirm it's age of check in.
As an aside , if your DS finds the kids meals not enough for him I would suggest making full use of the buffet and "family style" meals as he can have as much as he wants. If he's on the childs cost for the dining plan ( which he is entitled to as it's age at check in) he would have to eat from the childs menu at the other full service meals.
Buffets off the top of my head are Bomas, Chef Mickey's, Crystal palace, Cape May Cafe, Donald's breakfastasaurus,trail end buffetteria, 1900 Park Fare and Hollywood and Vine .
Family style is Ohana's, Whispering Canyon , Liberty tree tavern , Princess story book dining and Cinderella's Royal table.
I think there may be a few more. I know that the buffet style isn't to everyone's taste (

) but I think there is enough variety and choice there to offer plenty of choice without having to worry about paying the extra $25 per day to "upgrade" the child to adult food costs. Plus I think it would be a massive headache to have the child in the reservations computer system as an adult for food costs and a child for ticket costs. I'll lay $100 it would blow a fuse in the reservation systems LOL