Well, B&J's factory tour in Colbyville and the Cold Hollow Cider Mill a couple of miles up the road are two of the most visited attractions. Moss Glens Falls(the one in Stowe) and taking a drive over Smugglers Notch is diferent and if ya don't mind spending a few bucks you can take the Toll Rd to the top(almost) of Mt Mansfield, the state's highest peak.
The pathway along Burlington's waterfront is awesome. If they like shopping a walk thru Church Street Marketplace might be worth it. The tour of Rock of Ages quarry in Granitville(near Barre) is cool and a walk thru Hope Cemetery(Barre) is truly unique.
this site has lots of info
http://www.travel-vermont.com/