If you get the dining plan, he will share you meals at most plated restaurants. At buffets, he can have his own plate and eat for free. At Cindy's castle (a plated meal) they still offered my son complimentary french toast sticks for breakfast, and he could eat the fruit and bread basket on the table for everyone. At ALL sit down restaurants I requested a glass of milk for him (fully expecting to pay) and it was just given to us. At counter service we paid for his drink if we got one.
HTH. Our ds was 23 months. We found the dining plan to be PLENTY of food for the 3 of us. By the time you get appetizer, meal, and dessert, you have more than enough to share.