Thank you for visiting us with your question, Jenni! We are delighted to have you here at the Disney Parks Moms Panel.
You know your son better than anyone, you know how much food will be enough for him and you may choose the right meal plan for your family needs. The Walt Disney World Resort has
three meal plans available, the most comprehensive being the
Disney Deluxe Dining Plan which will give each guest three meals and two snacks each night of their package stay. This plan does not restrict the type of meals you can get so you may choose to eat all you care to eat buffet locations or the regular sit-down restaurants, where everybody will get an appetizer, entrée, dessert and a beverage. If you chose to purchase the other meal plans available and it turned out your son's appetite is not satisfied, you can always purchase an extra item from the menu or bring one from home.
I am sure your son will be just fine, I bet he will be more into the rides and attractions and will not care much about the food!
Jenni, I hope this information helps you guide your planning. I hope you have a memorable vacation with your son!
See you real soon!
~Desiree