I assume you have a week for the trip, so you may not be able to add too much in. Would agree with the ones who suggest Gettysburg, though it will be a little bit of detour off your route. However, as long as you are in the Williamsburg area, be sure to spend a day visiting Jamestown and Yorktown. The kids will likely find the Jamestown "settlement" more interesting than the actual site - the former is a "living history" park with reconstructed Indian "village," pioneer buildings and ships (full-scale replicas of what the English came over in). Very instructive and fun. The latter is more of an archeological dig. Yorktown is one of the few battlefields that saw action in both the Revolutionary and Civil Wars. We did not go to the visitor center there, so can't comment on that, but I was impressed with the construction of the redoubts. Makes history come more alive - as do visiting Williamsburg itself, and the Jamestown settlement.
