Hey there, Karen!
A lot has changed since I had my gastric bypass surgery 10 years ago, but there have been many wonderful meals at
Walt Disney World in that time. The best advice I ever got was to not limit myself to eating kids meals. While you will find that Walt Disney World has some really healthy children's meal options, you might miss out on some truly delicious grown up options.
In all of my years since bariatric surgery, I've only had one table service restaurant tell me they don't allow adults to purchase children's meals, so I will say your mileage may vary when it comes to this. Quick Service meals won't be an issue, but you may want to explain to your server a need to order the kids meal at a table service location. At the moment, there is no option to pay children's prices at buffets or all you care to eat meals.
I also encourage you to note on all of your dining reservations that you have a
special dietary need. The culinary team at the Walt Disney World restaurants may be able to adapt something on the adult menu or offer suggestions for something they can prepare for you that will work with your new stomach.
Welcome to "loser"ville, and I hope you find you can still enjoy some of your Walt Disney World vacation favorites when you get there!
Anna