"Let's drive all the way to New Orleans," says four-year-old Alison. The sign on the front of her bus, made up of genuine pieces or retired Metrobuses, reads Farragut Square. But the Capital Children's Museum, home of the bus and dozens of other "experiences," lets kids go as far as their imaginations will take them.

On a typical Saturday morning, Andre, seven, straddles a Harley-Davidson police motorcycle, making appropriate noises, while Ariel, 1 1/2, perches precariously on the fender behind. Others fiddle with the inner workings of traffic lights and fire-alarm boxes, while a Cub Scout den from Alexandria learns how to work the computer.

"Hey, look, we're in Chinatown," says four-year-old Tabitha, pointing excitedly to a street sign in Chinese characters. They are really in the museum's city room, a collection of things kids can only see in the city but can play with at the museum.

Meanwhile, in the forest room, a crepe-paper jungle, Geoffrey's eight-birthday party is breaking up. His 2 1/2-year-old sister, Missy, takes off the sunbonnet and old-fashioned dress she borrowed from the museum's collection, and the party goes home for ice cream and birthday cake. (No eating is allowed at the museum, and birthday guests are supposed to clear out before the museum opens to the public.)

"Who do you want to make a valentine for?" a volunteer asks three-year-old Amy. Amy wants to make several. She rubs one stamp after another into red paint and creates impressions of broken hearts and giraffes on white paper. The stamps, the volunteer explains, were made at the museum out of old carpet scraps. In another part of the craft room, Kristen, seven, and Emily, four, are making crayon rubbings of the soles of shoes and of pieces of ornamental metal.

Miriam Grunfeld, the museum's chief staffer, walks through announcing that Nestor the Magician, a local high-school student, is about to start a magic show in the city room. The other rooms empty momentarily as kids stream to the small stage to watch the prestidigitation. But, also as if by magic, the other rooms quickly fill up again. New people keep arriving, neighborhood kids in small clutches, suburban families in station-wagon loads.

In a room filled with levers, pulleys and gears, 1 1/2-year-old Caroline concentrates on fitting a stick of bamboo into a rubber socket, the first step toward a sort of geodesic dome. A little boy sits on what looks like a swing, but is really a scale, while a volunteer piles bricks and bags of sand on the other side. "This is how much you weigh. Can you pick yourself up?" says the volunteer, handing the boy some 35-pounds-worth of sand and bricks.

"Here you go, ma'am, eight cents," says a little girl sitting behind a real cash register filled with play money as another littler girl checks out a huge order of groceries. Another customer just buys a box of cocoa, which she pretends to cook on an old-fashioned stove.

"Do you guys want to go higher or put a roof on?" a volunteer asks a crew building a cabin out of supersize Lincoln logs. When the cabin is about five feet tall, they decide to put the roof on. Kids of all sizes climb in through the windows and door. A mother trying to go home finally finds her youngest inside.

"Oh, no!" cries Grunfeld as she discovers another stray: One of the birthday guests has been left behind at the museum. The kid grins - he doesn't mind a bit.