The Montshire Museum of Science sits just over the Connecticut River from Hanover and is one of the best family attractions in the Upper Valley. Its exhibits are hands-on rather than hushed, with plenty of room for children to test, build, turn, splash, and ask questions.
The outdoor grounds matter almost as much as the galleries, with trails and seasonal water exhibits that make the museum feel less boxed-in than many science centres. It is a very good rainy-day option, but it also works when the weather is clear.