Here are some ideas -
Billings Farm Museum, Woodstock Vermont. This is an 1800's working farm setup as a museum. Wagon rides, animal demos, ice cream making, etc, etc. Great fun for the family. Across the road is the Rockefeller Estate national park, with a mansion and great walking trails.
Ben and Jerry's factory tour, Waterbury Vermont.
Rock of Ages stone quarry, Graniteville Vermont.
Mt Ascutney auto road - Ascutney Vermont. You can drive close to the summit for an amazing view of both Vt and NH. Nice hiking trails abound.
Alpine Slides - at many ski areas, like Killington, Pico, Bromley,etc.

Will second the Billings Farm as a family activity -- very good. The Marsh/Billings/Rockefeller park across the street is not as kid-oriented, but the mansion is excellent to tour. Reports earlier this summer were to take usual precautions against ticks if you hike the trails.

Also second the Ben and Jerry tour, again well worth the visit. You'll also find the Cold Hollow Apple Cider Mill and a Cabot Cheese store outpost nearby.

Haven't been to the others.

There's a very good kid-oriented science museum in Windsor, the Montshire Museum.

The Montshire Museum is in Norwich, VT, not Windsor.

I saw on another thread you were considering Ben and Jerry's and the Teddy bear factory en route to Lake George. If you do travel across VT toward Burlington/Shelburne, the Shelburne museum is a good destination.

In Waterbury Center(near Ben and Jerry's and the Cider Mill) there is a glassblowing studio that was very interesting to a friend's 10 year old daughter last summer.

Vttraveler correctly pointed out my mistake -- the Montshire Museum is indeed in Norwich. Sorry about that.

thank you all for your responses. looking into your great ideas