MAMALU PERMANENTLY CLOSED IN 2009.
Mamalu in Williamsburg, Brooklyn is a great place to spend a cold or rainy day with babies and preschoolers, and the best part is that you can stay as long as you like for just $5 per child. Located across the street from McCarren Park, it's very convenient to get to with a car, I always find parking right outside. You can also get there fairly easily on the L or G train but expect a few blocks of a walk when you get off the train.
The space is large and airy and nicely designed with murals and mobiles and divided in two with the cafe in front and the play area in back. What I like about the play area is that it doesn't have a lot of toys which lets kids run around and explore without feeling overwhelmed and the toys they have are kept clean and in good shape. One wall of the play space is filled with a huge blackboard which for some is great fun, but can also present a bit of a challenge for mouthy little toddlers who like to eat chalk though its easy enough to position yourself away from the chalk stash.