My 7 year old wouldn't go on the larger "scary" coaster at Dutch Wonderland, although loved the other rides (except the "baby" ones.) So I hope the rides are not a bust for you in that respect. I figure we have the entire 9-18 year age range to do big roller coasters. The waterparks will not be open yet for spring.
Feel sorry for the families who can't enjoy one day at Williamsburg. Does that mean London, Rome, Philadelphia, Tikal, Angkor Wat are a snooze fest for you too?
Don't go when it's hot, go for one day only, have great meals and skip some of the demonstrations. My young kids particularly enjoyed the gunsmith and the leather shop behind the armory for some reason.

Busch Gardens is awesome, they will enjoy it!