We were at WDW from 9/3 to 9/11, which was right after dd turned 10. Some places let her order off the kid's menu. Others did not.

The policy concerning an adult (in this case, a 10 y.o.) ordering a child's meal off of a menu with the DDP was inconsistent.
I had to pay OOP for a kid's meal at WCC because they wouldn't use an adult credit for a kid's meal and dd wanted the kid's meal. I thought that was crazy. Having dd downgrade her order to a kid's meal saved Disney money because the kid's meal would have been less expensive for them to provide than the adult meal would have been. I paid for the meal without a fuss as it wasn't expensive and I didn't want to make dd feel bad about wanting the kid's burger with fries, though it did rub me the wrong way that she couldn't downgrade to a kid's meal with her adult credit.
Also, I was told up front that she was required to order an adult meal at Chef's, though she wanted an adult meal there anyway. If she did want a kid's meal there, I would have had to have paid OOP there too.
OTOH, Le Cellier, 50's PT, and Coral Reef did allow her to use her adult credit for a kid's meal. In fact, the 50's PT server offered dd both menus and volunteered to do an adult portion of any item on the kid's meal for her, which was nice.
We also ate at 2 buffets and the Fantasmic Dinner Package at Mama Melrose's for which she was rightfully charged as an adult.
In short, 2 restaurants did not allow 10 y.o. dd to order off of the children's menu with her adult credit, though 3 restaurants did.