Hi, Kristi!
Been there!
When you book Cinderella's Royal Table, you'll have to include your son as an adult on the reservation, and pay accordingly. However, this may actually end up being a good thing in the long run.
Once my son was considered an adult on our Disney Dining Plan (he's 11 now, too), it actually opened up options that may not have been investigated had he been solely looking at the kids' menu. At many table service locations, we've explained that our younger eaters (or even my sometimes-finicky husband) simply don't see anything on the traditional menu that appeals to them, and the server has been very helpful in finding an alternative (often from the kids' menu). An adult-sized portion of some items from the kids' menu can sometimes be substituted for an entree or a side dish or two, if you simply ask. Take a look at
Cinderella's Royal Table's menu for a better idea of what your little prince may be interested in ordering.
Enjoy your meal in the beautiful Cinderella Castle, Kristi! Be sure to send more questions as you think of them; we love to help!