Same here...we use the DDE and both my girls are preteens, and all three of us have ordered from the kids menu before.
With the dining plan they don't care if an adult (i.e. over age 10) orders from the kids menu because the adult credit cost more.....but they won't allow a kid (i.e. age 3-9) to use credits to order from the adult menu (because their plan was lower priced). That makes sense of course.
My girls and I have also shared two adult meals between the three of us, quite often in fact. So if your kids want to eat the adult fare, but it's just too much food, just have them share. I have never been charged or turned down when requesting an extra plate so that we can divy up the foods. It's also a great way for us to get to try more items! At TS places they will divide the food onto two plates for you if you simply say "these two will be sharing the chicken". Never been charged in a TS either, though I have read that some of the really fancy ones will charge a plate fee (I think it was V&A and CG). But, even that charge is likely to be less than ordering two entrees that neither child can finish, lol.