The tourists--bless their souls and their cash in our coffers -- are all over town for the duration now, guaranteeing that special seasonal opportunity to queue up in meet-the-horizon lines everywhere from the Archives to the Zoo.

And yet, you've promised the kids that this is their day. This is a Big Person Pledge, and therefore an unbreakable blood oath. Not to worry. The solution is simple enough: Become a tourist yourself -- in Baltimore. It's a great place to escape for a full, hassle-free day with the kids at: America's largest railroading museum, a streetcar museum, a vest-pocket firefighting museum and a zoo.

At the B&O RAILROAD MUSEUM, you can stand in the shadow of a giant General Motors diesel locomotive; check out Pullman lounge, dining and sleeping coaches; see the baggage car that carried President Eisenhower's casket on the nation's last presidential funeral train in 1969; and marvel at a 1907 tunnel gauger and a 1919 wooden snowplow -- all before you even get inside the museum. And inside is the real treat, a great museum that informs and inspires. There's history: The Mount Clare Depot site is the late- 1820s birthplace of American commercial railroading. There's straightforward fun: a collection of model trains and a working HO model railroad in a diorama of Paw Paw, West Virginia, complete with mountains, tunnels and river. There's education: how track is laid and bridges are built. There's romance: a love for the muscular steam beasts that labored to build America and the ribbons of rail that brought escape and adventure. And there's the grandeur of the Round House, with its magnificent reach toward the sky, its historical displays and its terrific collection of engines, coaches, cabooses -- many of which kids from 1 to 100 can climb aboard and dream upon. Through it all, a fine imagination is at work: Stage coaches adapted as rail cars and a Conestoga wagon are part of the display, as is a kind of steam kettle on wheels based on speculative writings of Sir Isaac Newton. After that can't-miss outing, if you've still got rail fever, you can head on over to the BALTIMORE STREETCAR MUSEUM for a ride in an open-air trolley, a look at about a dozen restored streetcars and a display of memorabilia, including 1926 advertisements in the Baltimore Sun proudly proclaiming that "streetcars make the suburbs possible."

On a recent outing, the kids, as might be expected, got the biggest kick out of the ride, watching the conductor ring up fares while the operator hustled along at heady speeds of up to 15 miles an hour that swept the fragrance of honeysuckle through the car. And then, as luck would have it, at trip's end a Chessie diesel thundered by on a nearby bridge, its engineer and crew waving to fans of an earlier era.

From there, you might consider a quick trip to the quiet little Baltimore City Fire Museum, housed in a building built in 1853 and featuring a 117-foot fire-watch tower modeled on Giotto's campanile in Florence.

The building, an active fire station until 1976, now houses three old pumpers (one from 1848), other old firefighting equipment from axes to a fire-alarm tape machine, relics of the great Baltimore fire of 1904 (which destroyed 1,343 buildings and burned all or part of 86 blocks), and a working spring-wound fire-alarm box with flashing blue light that the kids will set off as long as anyone can stand it.

Part of the place's charm on a recent Sunday rested with the two enthusiastic pre-teen youngsters serving as junior docents, leading the kids around and whispering of ghosts in the tower -- four firefighters killed in the rush to a false alarm. The rest can be attributed to the easy atmosphere and the eclectic displays, among them a March 7, 1913, photo of the burning SS Alum Chine, which blew up with 360 tons of dynamite aboard.

A final stop might be the BALTIMORE ZOO. It stands deep in the giant shadow cast up the parkway by the Washington Zoo, and can't begin to compete with the scope or quality of the Smithsonian-run colossus. But it does make a special effort to appeal to kids. There are swings, climbing bars and picnic areas, a "Zoo-Choo" and merry-go-round (each 30 cents a ride), a playground (with red caboose and rocket slide) and a petting zoo where a youngster can grab a handful of yak hair to bring to show-and-tell. (There's also a free double-decker shuttle bus running between the zoo and the aquarium. It runs only weekdays now, but will run daily during the summer, starting May 28.)

The Washington Zoo, in its richly funded enlightenment, has tried to put its animals in their natural habitats, with the result that many cannot be seen close-up. But at the Baltimore Zoo, which struggles mightily to stay half-a-step ahead of scruffiness, most animals are still in old-fashioned cages, meaning you can practically reach out and touch a tiger or leopard.

At its masterfully arranged new lion habitat, you can peer through special windows for a startlingly close but unobtrusive look at the king in his kingdom, stretched in graceful repose, his elevated throne a driftwood tree.

The zoo is proudest, however, of its colony of African penguins -- a type that is under two feet tall. Their 3 o'clock feeding is a daily hit as they waddle-strut their way to belly-flopping entries and then course through the water like a tightly organized fighter squadron. They're sport fishermen of the first order -- if they don't get to a fish before it hits bottom, they let it go for a later day, preferring the race and catch.

And when that last race is run, they head single-file into their nests like nuns on their way to vespers.

There are other lingering memories: The cool spray of a filling pool as a hippo placidly debates its entry;;the zoo- choo's whistling salute to the ostriches; the boy riding the zebra and the girl on Big Bunny, rising and falling like all self-respecting members of a merry menagerie, chasing each other round and round, never gaining but never retreating.

A reminder that you can't lose when you go to the zoo. KIDDING AROUND IN BALTIMORE B&O RAIROAD MUSEUM -- 901 West Pratt Street, open 10 to 4 Wednesday through Sunday; closed major holidays. Admission is $2 for adults; $1 for children 12 and under. To get there: From Pratt Street, go one block north to Lombard, turn left on Lombard to Poppleton, then left on Poppleton and straight into the museum parking lot. For information, call 301/237-2387. BALTIMORE STREETCAR MUSEUM -- 1901 Falls Road, open noon to 5 all year on Sundays. In June, July and August it's also open Thursdays 7 to 9 p.m. and Saturdays noon to 4. Free admission; trolley rides $1 for adults, 50 cents for children four through 11, under four free. From Pratt Street, turn left on Charles Street to Lafayette, right on Falls Road. For information, 301/547-0264. BALTIMORE CITY FIRE MUSEUM -- 414 Gay Street, open Thursday 11 to 2, Friday and Saturday 7 to 9 p.m., and on Sundays (if the volunteers can make it) 1 to 4. Free. Take Pratt Street east to Gay, left onto Gay. For information, 301/727-2414. BALTIMORE ZOO -- At Druid Hill Park, open daily from 10 to 4:20 (to 5:20 on summer Sundays beginning May 29). Admission is $1.50 for adults, 50 cents for children (2-11), $1 for 0ver-62s. From Pratt Street, turn left on Gay and go north to Jones Falls Expressway (I-83), north on I-83 to Druid Park-Lake Drive exit, follow zoo signs. For information, 301/889-9444.