They should have card from their dr. I have a card from the manufacturer of my lap band that shares a little info abou the surgery and shares how my stomach won't hold a normal adult portion and suggesting that I be allowed to eat from the children's menu. Most TS have one unique item to that restaurant. I am not sure what I am going to do, but I will be asking if there is a child's meal that I would eat...like at Cali grill. Right now I can only fit 1/2 to 3/4 cup of food in for any meal with no drinking while eating allowed.
On the DDP my son has asked for a childs meal though an adult, they prepare it in a double portion and charge an adult price.
OP, ordering a child's meal form a CS will not be an issue. THey don't care who eats it once it has been purchased. But your choices will be limited at many. SOme mroe interesting ones would be Sunshine Seasons by Soarin, I love the grilled cheese pretzel (though it now has too much bread for me to comfotably consume without sliming and PBing) in the sand bucket at the water park, yak n yeti, Flame Tree BBQ, some of the hotel food courts are better choices.