I lived in Williamsburg for three years, and I currently live 2 hours away with season passes to Busch Gardens. Next to Disney, Busch Gardens is one of the best, most family friendly and well themed parks in the country. I highly recommend it. If you also are interested in Water Country USA, you can get a special 2 day ticket to both parks.
The posters that mentioned the Trellis are definitely correct. It is a fantastic restaurant and its chef did, in fact, invent Death by Chocolate. In addition to that, they have many other wonderful desserts. There are many nights when I have left the Trellis feeling as if I would explode, but never regrettuing it! It is not cheap (although no more expensive than most sit-down WDW restaurants), but if money is an issue I would highly recommend lunch. It is less expensive and still has wonderful selections. I also would have no hesitation bringing a young child in for lunch, as long as he or she has reasonable self control for that age. It is located near the end of Duke of Gloucester street closer to William & Mary.
Christiana Campbell's is our favorite tavern restaurant. While it is similar to the others, it has more of a seafood bent. If you go, make sure you have the spoon bread.
If you are looking for a quick, inexpensive bite to eat, be sure to go to the Cheese Shop. It is a little gourmet shop that makes the best sandwiches. It is located across the parking lot from the rear of the Trellis.
I hope you have a great trip!