Thank you! You mentioned southern Vermont. Do you think there are some more things for children there compared to western Massachusetts?

No more, no less. I mean people live in those places :-) year-round. Kids live there -joking around, but true. What do they do for fun? You could find kid-centered activities to do anywhere you choose in New England. Of course places with streams, lakes, mountains, parks, probably more interesting to a kid then cities or towns? There's the Ben & Jerry ice ceam factory tour (just kidding around, but truly pick a couple places you are considering and look up the towns. Like for western Mass, use Northamptom and Amherst. For southern VT use Brattleboro and Bennington.
Happy planning!

The drive between Brattelboro and Bennington is especially scenic

Yes, and if you turn northwards most of the state is lovely to drive through.

I second the Lake George area but would add in Saratoga NY. If you go during racing season you can do a morning paddock tour and the kids can get to see the horses up close. Even race day is a ton of fun. Get at table and have a picnic, there is a play area. Saratoga Race Course is nothing like the ones in NJ and it makes for a very fun day. You also have Saratoga lake, a small rodeo during the week and a childrens museum, Happy planning .

Yes Saratoga is awesome to visit and I've done the morning paddock tour, nice experience. Saratoga during racing season is generally pretty pricey though. You will want to stay someplace with a pool with kids.