Hi Margaret! It is hard planning when you know the little ones will have a tough time adapting to changes in their schedule and meals. It is best to come prepared in all ways.
First of all be aware that rooms will have only small refrigerators unless you have booked a DVC room that comes equipped with a full kitchen. You can also book a Fort Wilderness cabin that has full kitchen. When doing your shopping you must be careful not to purchase too much that will need to be refrigerated.
There are small areas in every resort store that have snack type foods for sale but it is certainly not the choice of a grocery store. The closest full grocery store is just outside of the Lake Buena Vista area and it is a Winn Dixie.
The easiest way to purchase foods of your choice ahead of time is to use the local delivery service, gardengrocers.com. You can peruse the many choices of foods that they offer and they will deliver them to your resort so they are there when you check in. They get very busy so be sure and put your order and delivery date in as soon as you know. Be careful of the quantity you order as well. I once accidentally ordered 10 pounds of bananas!!!!! And yes they were all there waiting for me when I walked into the cabin!
Your final choice is to ship ahead non perishable things to your resort. The resorts have
Mail Services available to the guests which allows them to ship things ahead of time. Make sure you address it to the person the reservation is under as well as clearly write the word GUEST next to it. Also include the date that you will be checking in. We have done this many times to get diapers and baby foods and formula there as it is very bulky and hard to carry it all in a suitcase.
Hope one of these suggestions will ease your mind about a fussy little one who is traveling with you. You will have an unbelievable vacation!