My family has been to BG in Williamsburg many times. It can be rough on the feet and legs if your are a couch potato. I don't exercise (EVER), and I was fine everytime. Most major theme parks are like this.
We usually stay at my father-in-law's time shares. We've stayed at Powhatan Plantation, Governor's Green, and Kingsgate. Powhatan Plantation is a bit farther away from things than the other two. With little ones it's nice to have the kitchen even if it is small. Laundry facilities are also a plus with little ones. I'm sure you can stay at one of these places if you're not a member. It will probably require one of those boring tours and meetings though.
Oh, there's also a Great Wolf Lodge in Williamsburg. It's pretty pricey so I've never stayed there. We did go take a walk around inside though. They have there own water park right inside the hotel. That's why it's so expensive. They also have themed rooms with little areas for the kiddies like a bear cave or log cabin. Pretty cool! We were going to go shortly after we visited, but I got pregnant with our 3rd and that cancelled it. Still looking forward to going someday!