Most table service restaurants will let anyone (adult or older child) order from the kids menu, but once in a while someone will post that a restaurant or server adhered to the 3-9 years old ages on the kids menu. Usually this was at a third party restaurant, but it is best to ask before ordering.
As far as upsizing the kids portion, that will also depend on the restaurant. You can ask if they will do it, especially if you are planning to use an adult dining credit for the meal. If they will not, you would probably be better off paying out of pocket for the kids meal and save the adult credit for another meal or 2 credit meal since the value of an adult table service credit is approx $37.50 and the OOP cost of a child's meal is far less than that.