There may be no such thing as a free lunch, but at the Art Barn this Saturday families can picnic and dabble in some free creativity at the "Eighth Annual Children's Art Festival." The Rock Creek Park gallery will offer beverages, art supplies and instruction gratis as children explore ceramics, calligraphy, prints and more.

An exhibit of 150 children's paintings will also be on display outside and a wide variety of entertainment will be staged throughout the day.

All the following events are free unless otherwise noted.

NATIONAL ZOO -- Open daily; gates open from 8 to 8; animal buildings, 9 to 6; panda feedings, 11 and 3; elephant training demonstrations, 2; Sea lion training demonstrations, 2, 3001 Connecticut Ave. NW (Rock Creek Park), on the Metro Red Line. Family learning centers Zoolab and Birdlab open Friday through Sunday, noon to 3; Herplab open Wednesday through Sunday, noon to 3. 673-4717.

OXON HILL FARM -- Open daily, 8:30 to 5, Oxon Hill Road (take Beltway exit 3A, turn right on Oxon Hill Road). Saturday, 8 to 11 p.m., "Barn Dance," take part in a square dance for families at the activity barn. Sunday, 1 to 3, "Tobacco Transplanting," take a tractor-drawn hayride to see how tobacco is transplanted using old-fashioned equipment. 839-1177.

NATIONAL AQUARIUM -- Open daily, 9 to 5, Department of Commerce, 14th and Constitution Avenue NW. The sharks are fed Monday, Wednesday and Saturday at 2; weekday features are a touch-tank, mini- theater and a thousand types of marine life. School groups should schedule in advance. Adults $1; children 50 cents. 377-2825.

CEDAR HILL -- Open daily, 9 to 4, 1411 W St. SE, Anacostia. Cedar Hill, Frederick Douglass' home, recalls his work with films, interpretive exhibits and a house tour. 426- 5961 or 426-5962 or 426-5963.

FRYING PAN FARM PARK -- Open daily, 10 to 6, 2709 West Ox Road, Herndon. A working model farm with animals such as goats, rabbits and peacocks. Tours for groups of ten or more may be arranged. 437-9101.

USS BARRY -- Open daily, 10 to 5, Washington Navy Yard, Ninth and M streets SE. The Navy destroyer's weather deck is open for public viewing and self-guided tours. 433-3377.

CHILDREN'S MUSEUM -- Monday through Saturday, 10 to 4, Sunday 1 to 4, Rose Hill Children's Museum north of Frederick, Maryland. Take U.S. 15 north to Exit 8 to Motter Avenue; follow Motter to left onto 14th Street and left onto North Market Street, follow signs to Rose Hill. Costumed tour guides conduct tours of the 1790 mansion. Hands-on exhibits include a loom, antique toys and spinning wheel. Adults $1; under 17 free. 301/694-1646.

DISCOVERY THEATER -- Friday, 10 and 11:30; Saturday, 1 and 3: Arts and Industries Building, 900 Jefferson Dr. SW. "Just So Stories." The Mermaid Theater of Nova Scotia performs Rudyard Kipling's classic children's tales; for children in kindergarten through fourth grade. $2.50, discounts for families and groups. 357-1500.

CAPITAL CHILDREN'S MUSEUM -- Daily, 10 to 5, 800 Third St. NE. Saturday and Sunday, "Celebrate the End of Spring" by making a stencil print. Admission $2. 543- 8600.

DOLL'S HOUSE & TOY MUSEUM -- Tuesday through Saturday, 10 to 5; Sunday, noon to 5, 5236 44th St. NW. A collection of antique dollhouses, dolls, toys, games and an exhibit of antique cat games and toys. Adults $2; under 14, $1; group rates available. 244-0024.

NATIONAL COLONIAL FARM -- Tuesday through Sunday, 10 to 5, 3400 Bryan Point Rd., Accokeek. Sunday, 1 to 4, "Colonial Basketry," learn how to make a basket using local materials. Adults $1; children under 12, free. 301/283-2113.

CLOISTERS CHILDREN'S MUSEUM -- Wednesday through Friday, 10 to 4:30; Saturday, 12 to 4, 10440 Falls Rd., Brooklandville, Maryland. Saturday, 2, "Eagle Dance," the Red Shield dancers perform hoop dances in traditional American Indian costume; Indian exhibit featuring artifacts, jewelry and beadwork. $2 donation requested from adults. 301/823-2551.

RAILROAD STATION MUSEUM -- Wednesday through Saturday, 11 to 4; Sunday, noon to 5, Main Street and Maryland Avenue, Ellicott City. The renovated station has a diorama of the trip of Tom Thumb (an early 19th-century train) from Baltimore to Ellicott City. There are also sight and sound shows, model train exhibits and tours of the museum. Adults $1.25; under 13, 75 cents. 301/461-1944.

COLONIAL FARM -- Wednesday through Sunday, 10 to 4:30, Claude Moore Colonial Farm at Turkey Run, 6310 Old Georgetown Pike, McLean. Take a self-guided tour of farm life for a low-income family in Colonial Virginia. Demonstrations of agricultural and domestic chores, such as spinning and candlemaking, round out the history lesson. Adults $1; children under 12, 50 cents. 703/442-7557.

ANACOSTIA NEIGHBORHOOD MUSEUM -- Friday 10 to 6; Saturday and Sunday, 1 to 6, 2405 Martin Luther King Jr. Ave. SE. Afro- American history lectures to ages four through eight as well as group tours and teaching services. 287-3369.

YOUTH DEMONSTRATION -- Friday, 6:30 to 9, Capitol Hill Arts Workshop, 545 Seventh St. SE, An evening of music, theater and artwork; at 7, you have the choice of seeing excerpts from "Free to Be You and Me," performed on stage or listening to music in another studio. Saturday, 10 to 5, "A Day of Dance," watch tap, break and modern dance, ballet, acrobatics and more. Free but reservations recommended. 547-6839.

CHILDREN'S RADIO THEATER -- Saturday, 8 a.m., WPFW 89.3 FM. "Brementown Musicians," an adaptation of the Grimm fairy tale. Listeners can participate in a call-in following each program by calling 783-3104.

BIRDWALKS ON ROOSEVELT ISLAND -- Saturday and Sunday, 8:30, Roosevelt Island Parking Lot, by the bridge, George Washington Parkway (northbound side only). Bring binoculars, wear subdued clothing and learn what birds look like and how they sound. Reservations required. 285-2598.

BATTING PRACTICE -- Saturday, 10 to 3; Sunday, 1:30 to 4:30; Tuesday and Thursday, 3 to 7:30, Tucker Road Community Park, 1771 Tucker Rd., Fort Washington, Md. Batting cage and automatic pitching machine; bats, balls and helmets provided. $1 for 20 balls; team reservations. 301/248-4404.

COMPUTER CARNIVAL -- Saturday, 10 to 4, ComputerKids, Wintergreen Plaza, 833 D Rockville Pike, Rockville, "Computer Carnival," with clowns, balloons, computer contests and software demonstrations for all ages. 279-5556.

ROCK CREEK NATURE CENTER -- Saturday, 10, 5200 Glover Rd. NW. "Tree Identification Walk." Join a park naturalist for a two-hour walk through the woods to learn about local trees. Sunday, 10, "Urban Wildlife," following a slide show and discusson, a park naturalist takes you on a walk to learn about area animals. 426-6829.

TROLLEY MUSEUM -- Saturday and Sunday, noon to 5, Northwest Branch Regional Park, Bonifant Road between Layhill Road and New Hampshire Avenue, north of Wheaton. Trolley rides: $1 adults; under 18, 75 cents; under two, free. 384-9797.

CHILDREN'S ART FESTIVAL -- Saturday, noon to 4, Art Barn, Rock Creek Park, 2401 Tilden St. NW, "Eighth Annual Children's Art Festival." In addition to an exhibition of children's art, kids can create their own pictures, ceramics, prints, calligraphy and more at the gallery; supplies free of charge. 426-6719.

SCHOOL CARNIVAL -- Saturday, noon to 5, Noyes Elementary School, 10th and Franklin streets NE. Children's games, rides and food. 576-6071.

CHILDREN'S PLANETARIUM -- Saturday and Sunday, 1 and 4, Rock Creek Nature Center, 5200 Glover Rd. NW. First show for children four to seven (must be accompanied by an adult); second show for ages seven and up. No latecomers are admitted. 426-6829.

ADVENTURE THEATER -- Saturday and Sunday, 1:30 and 3:30, Adventure Theater, Glen Echo Park, Glen Echo, Md. "Charlotte's Web." $3, group rates available. 320-5331 weekdays and performance days from 10 to 2.

WOODLEY PARK BLOCK PARTY -- Sunday, 1 to 5, 2800 Block of 27th Street NW (between Cathedral and Woodley). Moon bounce, petting zoo, pony rides, music and more. 667-9240.

CHILDREN'S THEATER -- Sunday, 2, Weinberg Center for the Arts, 20 West Patrick St., Frederick, Md. (Market Street Exit off 270 North; go four miles to left on Patrick Street), "Cat-astrophe," a dance and drama performance by Dancers with Emotion- Lollipop Gang. $4.50; students and seniors, $3.50. 301/694-8585.