IN THE 1890S, when John Riley tended Lock 24 on the C&O Canal, the Seneca sandstone house beside the lock was filled with his children, who fished and swam and helped tend the garden, feed the chickens and churn the butter.

But in 1905, three-year-old Catherine Riley drowned in Seneca Creek, and when another baby was born, Mrs. Riley insisted that the child must grow up away from the water. So, while John continued to tend the lock until the canal shut down in 1924, the family left the house for a home on nearby River Road.

Now, four score years later, Riley's Lockhouse is again filled with children -- Brownies and Girl Scouts in 1890s dresses -- who make the old lockhouse come alive for visitors every Saturday and Sunday from 1 to 4.

"This is the boys' bedroom," nine-year-old McKaylee Kerwin explains, leading visitors up the stairs to the two low-ceilinged bedrooms. "The littlest ones slept with the Mommy and Daddy."

Meanwhile, down in the parlor, Jenny Wildt, 6, and Anne Weirich, 7, are looking through a stereoscope, which showed the first 3-D pictures. Katie Dye, 8, is sweeping the mud out of the entryway, and Kathryn Wildt, 8, is showing visitors through the kitchen.

"This is the pie safe," she says, "where Mrs. Riley used to keep their pies because they didn't have a refrigerator."

The furniture in the house is Victorian but not the original Riley furniture, explains docent Marcia Bell. That furniture is now in the home of Helen Riley Bodmer, youngest of the Riley children, who lives nearby in Seneca. Her brother, Raymond, also lives in Seneca and often drops by the house when he goes fishing, says Bell.

"A canal is a great big ditch," explains the docent, leading some of the Brownies outside to the banks of the ditch, "and a lock is a step that takes the barges uphill. . . It's just like a staircase, except the stairs are filled with water. The barges used to carry sandstone, which is what this house is made of, plus grain and coal and whatever people wanted to ship. There's a great big pond down there where the barges would wait."

The lockhouse came with the job -- which paid $35 a month when the barges were running, $10 in the winter months -- and carried the right to firewood and an acre of land for garden and room to pasture livestock. It was originally whitewashed, the better to be seen from a distance by boat captains. The whitewash has weathered off the 20-inch-thick sandstone walls, and Bell points out the stone just above eye level that bears the date, 1829, the year the house was built. The house never had any plumbing, electricity or telephone service -- although a phone line was strung along the canal in 1879. The Rileys used a wood stove for cooking and heat, and oil lamps for light. Drinking water was carried from a spring.

The wood stove no longer works, so Kevin McCormally, the husband of a Brownie leader, is chopping wood to build a fire outside. When the fire is hot, the girls make apple butter on a grill set up over the fire. The Rileys, according to Raymond Riley, used to make apple butter in a big iron pot. Since the Brownies are using a flimsier cauldron, they add a little apple juice to keep the apples from burning.

When the Rileys lived here, the kids helped make sauerkraut from the cabbage grown in the garden beside the canal. Mrs. Riley did a lot of baking and often sold baked goods to barge families and neighbors. Everybody pitched in to churn butter, and on summer Sundays everybody took a turn at the crank and made ice cream. The Brownies all take a few turns crushing and stirring up the apples and adding cinammon. But they tend to wander off to play marbles or checkers with checkers made of corn cob slices or to act as tour guides.

Although there's no barge traffic along the canal, there are a lot of hikers on the towpath where the mules used to walk, and many of them stop to tour the house and sample the food prepared by the girls.

On this day, they get steaming apple butter on crackers. Next time it may be freshly churned butter offering a taste of the way life used to be beside the C&O.

UNLOCKING THE LOCKHOUSE -- Riley's Lockhouse is free, and open every Saturday and Sunday from 1 to 4. There is a docent present during those hours to show visitors through the house and explain its history. There are usually Brownies or Girl Scouts in period costume to help recreate the time when the Rileys lived there. Visitors are invited to join the girls in their games and to share the food they've made.

The program is administered by Girl Scout volunteers as a living history program. For information on how Brownies and Scouts can participate, call Cathryn Finch at 654-7522.

The lockhouse makes a good stop on a hike along the towpath. It's .7 mile from Violettes Lock; 3.2 miles from Pennyfield Lock, and six miles from Swain's Lock, all of which are accessible from River Road.

GETTING THERE -- To get to Riley's Lockhouse by car, take the Beltway to River Road and head toward Potomac. After about 12 miles, where River Road appears to dead end, turn left and go about 3/4 of a mile to Riley's Lock Road. Turn left and go to the end of the road.