Smithsonian National Postal Museum

Loaner cribs, baby baths and swings at the front desk, so you can pack less. Ask ahead, there are only a few.

Step into picture-book worlds and read, sketch and build inside them. It's pitched at kindergarten through third grade.

A tall Wallholla climbing tower packed into a small city park. The tower is what school-age kids head for.

A glasshouse of tropical plants and desert displays, so kids can go from jungle to cactus in a few steps.

Galleries inside and a sculpture garden outside, so when kids are done with paintings there is room to walk among the big pieces.

Portraits and a courtyard, plus Explore, a hands-on space for 18 months to 8, so the youngest have their own room.