Just to add to one of the points mentioned above-some of the TS restaurants do offer a Junior sized portion of kid's meals. We did this last year at Kona and 50's PTC. DD10 turned 10 during our trip so I had her as an adult for credits but sometimes she wanted one of the kid's meals. They basically can supersize some of the kid's meals to give you more. Of course, since you'll be wanting smaller servings than that may not matter to you.
Back in Jan. 06 my family went without the DDP. We ate at HBD one day for lunch and due to the heat and my DSis' not liking anything too different, 3 of us adults ordered off the kid's menu. We all got the chicken. It was basically a small chicken breast, with no sauce, delicious, but a little bland. I see now that they offer one with BBQ sauce.(you could get sauceless I'm sure) Our server told us we could double or triple our kid's chicken if we wanted. I don't think it's that unusual that guests order from the kid's menu.
As far as many of the kid's meals being high in fat, this can be true at some. for example at Kona the kid's choices are: hot dog, hamburger, mac 'n cheese or ravioli. If I was trying to eat with less fat, smaller portions, etc. I would probably not order from the kid's menu there but order the Tuna Oscar instead which is basically rare, seared tuna, no sauce.
Oh, and one time when we were at Kona my sister mentioned to the server that she couldn't eat any crab and wanted to make sure whatever she was ordering (I can't remember what) had no crab. The chef made a visit to our table to discuss her dining choices. (This totally embarrassed her, BTW). I believe you can do this at most TS. Ask if you can order a meal special, or see if you can speak with the Chef.