“If nothing else, we can always go to Marbles.” Many consider Marbles the best place to bring kids whenever the weather is less than perfect, and it can get very crowded on a rainy weekend. That said, the place is large, with many different exhibits covering a sizable age range from just about 0 to 12 and older. Most exhibits have a clear educational character, and also a corporate sponsor, which keeps the admission at the small amount of $5 for non-members.
Before I had kids I would’ve been amused at the thought of bringing an 18-months-old to see a museum, but Marbles does manage to entertain and educate even the smallest ones. The Forest Room (take a left in front of the “bus” on the first floor) is awfully cute and quite new. 2-3yr-old kids will enjoy the section behind it, where you can mock-shop or play with an elaborate train set. There is water play and a pirate ship further in the back, and a small outdoors section. The upper floor covers everything from Sports, to Building/Construction/Crafts, to Money. There is also an IMAX with many documentaries, which I have not yet visited with kids.
A annual family membership is just $100, so you break even after 4-5 visits. There are additional membership benefits, and you support the long-term survival of this place.
Marbles is generally open 9-5, and closed Mondays. Check the website (with its slightly annoying sounds effects) for details and to verify hours etc.