Hi Cassondra,
Hooray for first vacations! I hope you and your family have a magical vacation!
In general, the policy is that everyone on the reservation must be on the same package. This means that if your family is all on the dining plan then everyone on the reservation must be on the plan as well.
However, given your son's medical condition, I would call Disney at 407-WDISNEY and explain the situtation to them. They can help you figure out the best option for your family.
If you do need to bring Pediasure into the parks, you can pack a smaller cooler with you. Also, if you do not want to bring it with you, the Garden Grocer is an online grocer who can deliver to your resort. I did check and they do stock this item.
Finally, if your son is able to have a few food items while he is at Disney, please ask to see the chef. They are the coolest people and will go to any length to make your son enjoy his meal. My daughter has a shellfish allergy and we go to the clam bake at Cape May Cafe. The chef walks her around like she is a princess.
You can also email cast members at
specialdiets@disneyworld.com with any questions you have.
Have a magical vacation!
Beth