You're staying for the week? If so, put the kid into day camp for at least a day. I would suggest the Nature and Hike minor. The counselors really work the kids hard while having tons of fun. The very popular "Stage and Sound" and "Arts and Crafts" were created for wimps imho. Any other minor in between these two are still cool.
If you want to do things on you own with the 7 yo, the water park are nice but small. The fun zone is cool too but not that special. Boating in Rum Runner is a good way to spend a few hours. If the kid is into hiking (as a minority at this age), options are way open. Can he ride without training wheels? The Stowe Rec Path is the one of the best -- ANYWHERE. Bring a lunch, wear your bathing suits underneath and expect to make multiple stops along the way. Caving and rock hopping at the notch is tons of fun too, although 7yo may be a bit too young.
Here is a recent thread on the water slides: