Garden Grill is our boys' favorite restaurant and our arrival night tradition! We've been there twice this year, and both times our servers told our pre-teen "Disney adults" that they could have kids or adult items. They also offered our pre-teens the kids' dessert. (Of course, as OP mentioned, the price is still the adult price.) We also have a pre-schooler, so I'm not sure if that made a difference, but I thought it was nice that our server specifically told our older boys about this flexibility.
Same thing happened in other WDW restaurants. Our server would offer our pre-teens both adult and kids' menus, and tell them they could order from either.