D.W.
How old are the kids?
I grew-up in Virginia, and those are all great places to go. You may be hit or miss on the weather. You might want to see what the average temperatures are for the week you're looking to be there. Though Virginia is generally warmer than IL, riding a cool rollercoaster on a cold day could be tough.
Williamsburg, alone, could take a couple of days depending on how into the kids want to be. Be prepared to walk a lot. Depending on if you drive or fly, I'd always recommend areas such as Charlottesville (Monticello and University of Virginia), Lurray Caverns, Virginia Beach, even Northern Virginia for Mount Vernon and the DC area.
My husband and I took a vacation there (and to see my family) over the course of 5 days several years ago and were able to take a lot of stuff in - with small kids, it may be tougher.
At 2 and almost 4, our kids enjoyed the recent trip to see my family in the DC area a lot less than we thought they would.
Have a great time if you decide to go.