The Woods Hole Science Aquarium is a great place to bring the kids when it's raining and it seems like there is nothing to do. The Aquarium, established in 1885, is the oldest in America and badly needs updating. Owned by the United States government and run by the National Marine Fisheries, the exhibits stretch along a large U-shaped corridor and consist of fish that populate the waters of the Atlantic seacost north of the Carolinas.
The place was crowded on the day of my visit and it's no wonder because it's a cheap place to go with lots of kids. All you have to do is put a donation in the box and you're golden. There are more tanks of fish upstairs, displays of turtle shells, jaws of sharks and other fish, and audio visual displays. There is a small seal tank outdoors where you can watch the feedings at specified times.
I'd recommend a visit here. It's a pretty little town and you can see the drawbridge and the Woods Hole Oceanographic Society's visitor center as well.