Bronx
Brooklyn
Manhattan
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Staten Island

New York Transit Museum
Corner of Boerum Place and Schermerhorn Street, 718-694-1600
Catch a train to this historic 1936 IND subway station and museum in Brooklyn Heights, which features many interactive exhibits. It's a fascinating look at one of the world's most intricate underground public transportation systems. [2-4 years; 5-8 years; 9+ years]

Prospect Park Carousel
Willink entrance, at Ocean and Flatbush Avenues and Empire Boulevard, 718-282-7789
Cap off a day in the park with a $1.50 ride on one of the ponies that circle this famed merry-go-round, which was built in 1912 and is one of the only wheelchair accessible carousels in the entire world. [All ages]

Prospect Park Zoo
Prospect Park, 450 Flatbush Ave., 718-399-7339
Go see where the wild things are and watch your kids come face-to-face with prairie dogs and walk amongst some wallabies! Admission is $6 for adults, and $2 for children between the ages of 3 and 12. Those under 3 are admitted at no cost. The zoo is open 365 days a year. [All ages]

Brooklyn Botanic Garden
900 Washington Avenue, 718-623-7200
Take the time to smell the roses—and the slew of other beautiful flowers—offered here, where admission is always free for children under 12. Regular admission for adults is $8, but everyone gets in for free on Tuesdays, as well as on Saturdays from 10 a.m. to noon, as long as there's not a special event going on. Call ahead to find out if there is. [All ages]

Brooklyn Bridge Promendade and Pierrepont Playground
Furman Street at Pierrepont Place
Take a family stroll and check out some of the most memorable views of the city. Don't forget to wave to the Statue of Liberty or to stop by the playground to take advantage of its great climbing structures and swing sets. [All ages]

Brooklyn Children's Museum
Corner of Brooklyn Avenue and St. Mark's Avenue, 718-735-4400
This museum was specifically designed for kids, and is planned to reopen by summer 2008 after months of renovations. Among the museum's highlights are an Animal Outpost, a greenhouse and garden, a Music Mix exhibit, a stage to play around on, and a Totally Tots section, just for those under 5. Reopening in September 08. Admission is $5 per person; free for kids 1 and under.  [All ages]

Millennium Skate Park
Colonial Road, between 68th Street and Wakeman Place, in Owl's Head Park
Give your kids their daily dose of extreme sports. Children under 18 need a guardian's signature on an onsite waiver, which you should download and fill out ahead of time. Helmets, knee pads, and elbow pads are also required for those utilizing the facility. [5-8 years; 9+ years]

Historic House Trust of New York City
Explore one of the Trust's 22 historic sites across the five boroughs and you'll be taking a virtual walk through time. Step foot inside everything from a modest farmer's cottage to a luxurious, grand mansion, all while getting a taste for what life was like in the city a hundred or so years ago. Among the Trust's highlights in Brooklyn are the Old Stone House, where the lawns once served as the summer home for the Brooklyn Dodgers, and the Pieter Claesen Wycoff House, which was built circa 1652, making it the oldest structure in all of New York. [2-4 years; 5-8 years; 9+ years]

Indoor Recreation Centers
Get your game on by investing in your neighborhood's center, where you can open up a world of low-cost activities for you and your family. Run by the New York City Department of Parks & Recreation, there are conveniently located sites in all five boroughs. Memberships are just $50 a year ($75 if the center has a pool) for adults, with no charge at all for kids under 18. So for less than $7 a month, you can tap into your local center's pool, gym, dance studios, art studios, game rooms, basketball courts, and more. [All ages]

Street Fairs and Festivals
Hit the pavement and scope out some of the low (or no) cost street fairs, festivals, and performances that go on all year around the city, such as the Association of Jazz Festival on July 27th and the Manhattan Youth Fair on August 1, for example. [All ages]