M.C.
There is a website for planning a vacation.
http://www.colonialwilliamsburg.com/do/special-events/spr...
Colonial Williamsburg is like a shorter version of the National Mall, where there is a long blocked off area and lots of activities at certain times happening along all of it. When we went in June last year (100+ degrees!) it was a bit disappointing in the there was so much that the kids wanted to do and they were all overlapping or at different ends of the 'walk' so that you were literally rushing if not jogging to get to the next thing.
Technically you are supposed to buy tickets, but I have been there twice, and have found that if I just walk around and look at the activities outside, that no one has stopped and asked for proof of a ticket. We did buy tickets last year because the kids wanted to go see a chat with George Washington. (That guy was good! ) So to buy those tickets, you have to have the main tickets. There is also a carriage ride that you can take, but that can be pricey. There is also a ghost walk you can take, that I wanted to do, but my kids were young so I didn't.
When you buy tickets to Williamsburg, you can then get a discount to Jamestown. Since your kids ARE history buffs, I would try to do at least one of the living museums.
Bush Gardens is also about 2 exits from Williamsburg. That can be pricey, but if you are looking for a bit of 'non historical' fun, its right there too. ($30 a ticket)
Instead of Monticello, you might be able to do Mount Vernon. It is about 15miles (1 hour in DC traffic) outside of DC.