WE WERE RIDING through the Frederick County countryside on the Walkersville Southern Railroad when my son Aaron, 5, asked a probing question of the line's treasurer, an accountant named Paul J. Bergdolt. Aaron wanted to know whether the railroad had any cars from another perhaps more legendary line. "How about the Santa Fe?" he asked. To which the train official glumly replied, "They unfortunately don't come here."

Well, okay, no Santa Fe. But how about a converted World War II troop sleeper car, a 1949 bright red Wabash caboose, an open B & O flat car with wooden benches and a 1939 30-ton Davenport diesel engine? And how about an hour-long, eight-mile excursion on just such a train a mere hour's drive from Washington?

This may indeed be the space age, the almost year of Y2K, the era of Nintendo and DVDs. And yet, there is something about the slow, creaky rumble of a train that entrances children. The train virus seems immune to technology.

Aaron has a bad case. So whenever the opportunity arises, he is ready to ride. His brother David, 8, though "Star Wars"-fixated, is a willing fellow traveler. So one Sunday, when their Uncle Rich, also an ardent train buff, was in town with his son Jake, 7, daughter Kate, 2, and his wife Ruthann, the Walkersville Southern seemed like the ideal outing.

The passengers-only railroad is a private, for-profit corporation that has rolling stock and some that just sits idle on a siding right off Biggs Ford Road in Walkersville, a formerly tiny farm town that is gradually giving way to the suburbs. People actually own shares in the railroad, which has been operating since 1995, though financially it's a loser. In other respects, however, it's a winner, for the rail buffs who both ride and own the train, about 50 of whom take turns operating it for no tangible reward.

The passing scene along the four-mile track includes farms, cows, grain silos, a lime kiln, the Catoctin Mountains, woods, grade crossings, housing developments and the Monocacy River. The railroad's small station, built by the Pennsylvania Railroad in 1920, looks as if it were plucked from a model railroad layout. Next to it is a B & O sleeper car, circa 1920, converted into a gift shop.

Heading out, the boys chose to ride in the ex-Western Maryland Troop Sleeper, which has park-style benches that can seat about 50 passengers. On this day, it carried only our party of eight and one other family of three. On the return trip, the boys chose to ride in the cupola of the caboose.

The train rattled along the 1869 right-of-way at no more than 10 miles an hour. A volunteer flagwoman in a car drove from grade crossing to grade crossing with a hand-held stop sign to warn what few motorists there were of the train's approach -- also signaled by two long, one short and one long toot of the horn.

The Walkersville Southern is big on safety, which is a good lesson for kids. "Son, tie your sneakers," Bergdolt admonished David. "Safety first always on the railroad." The boys were also directed to keep their hands off the air brake lever, "which is to be operated by qualified railroad employees only," according to the posted sign.

The other hazard was yellow jackets, which were also riding with us. "Yellow jackets can kill a person, can't they, Dad?" Jake asked his father. Fortunately, there followed two loud toots from the train, which seemed to send them packing. "That scares the bees," said Aaron, relieved. Jake, from San Diego, wanted to know if there was air-conditioning. "You open a window," Bergdolt said.

In the caboose, the boys learned another lesson when Aaron asked about a sign that said "Bathroom Out of Order." Bergdolt explained that, for the train crews of old, cabooses were homes away from home, with stoves, bunks, and, yes, even bathrooms.

There's nothing quite like a real train ride, unless, of course, it's a room full of model trains.

So from Walkersville, we drove 22 miles south to Brunswick, a gritty old railroad town along the Potomac River, also in Frederick County. There the Brunswick Railroad Museum beckoned.

The kids weren't the least bit interested in the narrated introductory slide show on the first floor or the static exhibits on the second. They headed straight up the stairs to the third-floor layout. It is, indeed, a remarkable re-creation of the B & O Railroad line from Union Station to Brunswick, 56 miles compressed into a single room.

More than that, it is interactive in a way that computer games never can be. And while every sign on the railroad seemed to say no, don't do this or that, the big sign at the HO-gauge layout was a welcoming "Kids at Play."

There are 41 buttons to push, plus three switches to control and one knob to turn. One button makes pigs squeal, another lights the hobo fire by the Monocacy, yet another causes crossing lights to flicker as trains go by. "Oh, no, there's a fire in there," Aaron said, pushing a button that ignited a light inside a warehouse somewhere in scaled-down Silver Spring. "A train is coming, a train is coming!" he said, excitedly.

David, meanwhile, announced, "There's something going on in Germantown." Actually, it was Seneca. He pushed a button, and suddenly the stationary HO-scale people positioned at the creek seemed to come alive with sounds.

To allow for a kid's-eye view of the layout, steps are located strategically along the way. The museum also provides a third-floor view of real freight trains passing by Brunswick. "Hey, here's a real train," announced Lee Smith, a museum volunteer who also worked as a B & O freight agent for five years in the late '50s. "Where's he going?" Aaron asked. It was a single coal-train "helper" engine, "going back to the yard," said Smith.

The boys were there for longer than they were on the Walkersville Southern, and still they showed no signs of losing steam. But the afternoon was getting on, and so were we. To cap the outing, we walked around the corner to the Silver Rail Diner for ice cream and milkshakes. Then Uncle Rich took some pictures of the railroad station at Brunswick, which formerly boasted a major freight yard with a roundhouse. It is still a place freight trains rumble through and is also now an important commuter stop to and from Washington.

Not to mention a mecca for rail fans of all ages.

WALKERSVILLE SOUTHERN RAILROAD -- Ticket office is at 34 W. Pennsylvania Ave., Walkersville, Md. 301/898-0899. The railroad operates every Saturday and Sunday May 1 through Oct. 31, with departures at 11 a.m., 1 p.m. and 3 p.m. The railroad will run the "Santa Special" Dec. 4, 5, 11 and 12. Regular season tickets cost $7 for adults, $3.50 for children, and is free for kids under 3 unless they occupy a seat. The railroad is also available for charters and caboose parties.

BRUNSWICK RAILROAD MUSEUM -- 40 W. Potomac St., Brunswick. 301/834-7100. Open April to January. Admission is $4 for adults, $2.50 for children 6 and over. From June to the first weekend in October, the museum is open Thursdays and Fridays from 10 to 2, Saturdays from 10 to 4 and Sundays from 1 to 4. From the second weekend in October to Christmas, it is open only Saturdays and Sundays.