Hi, Jennifer! I'm so excited that you will get to enjoy the magic of Walt Disney World with your very own Prince Charming!
First, consider what your son loves. If he gets excited over pirates, you may want to get him a makeover at the Pirates League or take him on a Pirates and Pals Fireworks Voyage, where he'll get to meet some pirate favorites, take a boat out to see the Wishes Fireworks from the Magic Kingdom, and then enjoy a quick meet with everyone's favorite Lost Boy.
Book some of the character dining experiences to have him meet some of the characters he loves. You can arrange to speak with the chef to accommodate any special dietary needs that your son has, and in the event that he is not able to eat, they may be able to make special arrangements with you to charge only a nominal entertainment fee.
You might take him to the Hoop Dee Doo Musical Revue, a slapstick, vaudeville type show that is great fun. Again, let them know of his dietary needs in advance.
How about a birds' eye view of the whole Walt Disney World resort area? You can enjoy a quick trip in the Characters in Flight hot air balloon in Downtown Disney. It's a wonderful, once in a lifetime experience!
Check out some of the special tours available at the theme parks. I highly recommend the Family Magic Tour for kids this age, but you'll find the whole list by clicking
Disney Tours and Experiences.
The amount of food on the dining plan is pretty great, and it may work better for you to share your meal with him or just purchase smaller side dishes or soups for him to enjoy.
Have a wonderful vacation!