It's a great trip! Colonial Williamsburg is fun and educational, and there's also other fun activities in the area.
Check if they're doing a scavenger hunt or other special activities when you go. The scavenger hunt made things even more fun for my kids. I also signed us up for a couple of programs. Check in advance because you need to make reservations for them.
I got a groupon for Colonial Crossings of Williamsburg. I had a suite that included a full kitchen. It was a good choice for my family. If it's ok with your allergies, Food For Thought is a very popular restaurant in Williamsburg. I don't know if they take reservations. I would check because I had to wait awhile for a table.
If you're looking for something to do in the evening after spending a day at Colonial Williasmburg, there's a miniature golf course nearby. It's called Pirates Cove.
If you like go karts, bumper cars, bumper boats, and things like that, check out Go Karts Plus.
Busch Gardens is there, if you want an amusement park. That's an all-day visit, though.