As usual, I'm late to the party, but do consider Charleston, ma deah. It can be cold (in the 50s) by a Southerner's standards, depending on when in winter you're going. It's very walkable, very hsitoric, and there are things to do with children like a harbour boat trip, the aquarium, and museums. Tours to nearby plantations are available or you can rent a car if you're flying in. Just some thoughts.