Hello Rochelle,
Thanks so much for stopping by the Disney Parks Moms Panel with your question! I completely understand your concern about having to pay for your son's meal at the Character Dining location when he will not be eating anything from the menu or buffet. I wanted to be extra sure about the answer I gave you, so I called Disney Dining not once, but twice, and was given the same information both times. In fact, the wording the two Cast Members used was almost identical, so I'm guessing this is a standard procedure in their system for instances like this.
The Cast Members both said there should be no charge for your son at the restaurant. They recommended having your son listed as an infant when you make your dining reservations, and also having a special note added to your reservation stating your son is tube fed and would not be eating anything. Doing both should help make the dining experience as hassle-free and enjoyable as possible. If you have already made your dining reservations, I'd recommend calling Disney Dining (you can find that number
here) to see if one or both of these changes can be made before you arrive. You might also ask to speak with a manager when you check in to explain the situation just to be sure there are no surprises when the bill arrives.
I hope that helps, Rochelle, and wishing your family the most magical of Walt Disney World vacations!
Sending lots of pixie dust,
Beth