Children's theater takes center stage this weekend. The D.C. Artists-in-Collaboration are presenting a multimedia production based on fairy tales by the Brothers Grimm at George Washington University. The three-day performance combines Japanese koto music with modern dance and storytelling; parachutes are even used as moving sculpture. And over at Arlington's Lubber Run Park, "The Magical Pied Piper" runs the entire weekend.

Saturday is also children's day at the National Colonial Farm in Accokeek. Kids can take part in colonial games and activities, including wool working, marble making and picking vegetables for a traditional 18th- century meal.

All 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, on the Metro Red Line. Family learning centers Zoolab and Birdlab open Friday through Sunday, noon to 3; Herplab open Wednesday to 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, 2, "Horse Sense," a farmer explains everything you always wanted to know about horses; Sunday, 9, "Morning Chores," help a farmer milk the cow and feed the animals. 839-1177.

NATIONAL AQUARIUM -- Open daily, 9 to 5, Department of Commerce, 14th and Constitution NW. Sharks are fed Monday, Wednesday and Saturday at 2; weekday features are a touch-tank, mini-theater and a thousand types of marine life. Saturday and Sunday, 10:30, "Behind-the-Scenes Tour." See the aquarium's daily operations; must reserve 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, exhibits and a house tour. 426-5961.

FRYING PAN FARM PARK -- Open daily, 10 to 6, 2709 West Ox Rd., Herndon. A working model farm with animals such as goats, rabbits and peacocks. Tours for groups of 10 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 viewing and self-guided tours. 433- 3377.

CHILDREN'S MUSEUM -- Monday-Saturday, 10 to 4, Sunday 1 to 4, Rose Hill Children's Museum, north of Frederick. Take U.S. 15 north to Exit 8; follow Motter Avenue to left on 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.

CAPITAL CHILDREN'S MUSEUM -- Daily, 10 to 5, 800 Third St. NE. Saturday and Sunday, "Mexican Art." Construct your own pre-Columbian Mexican disk to hang on the wall or around your neck. Museum admission, $2. 543-8600.

DOLL'S HOUSE & TOY MUSEUM -- Tuesday-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- Sunday, 10 to 5, 3400 Bryan Point Rd., Accokeek. Saturday, 11 to 1, "Children's Day." Children ages eight to 12 can participate in a variety of colonial activities, including 18th-century games and preparing and eating a traditional colonial meal. Children's Day fee: $3.50. Admission other days: 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, Md. Saturday, 1, "Magic and Story Theater," an afternoon of folktales, magic tricks, comedy and drama. $2 donation requested from adults. 301/823-2551.

RAILROAD STATION MUSEUM -- Wednesday-Saturday, 11 to 4; Sunday, noon to 5, Main Street at 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-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. Ongoing demonstrations of agricultural and domestic chores, such as spinning and candlemaking, round out this history lesson. Adults $1; children under 12, 50 cents. 703/442-7557.

ANACOSTIA NEIGHBORHOOD MUSEUM -- Friday 10 to 6; Saturday-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.

THE MAMMALS THAT FLY -- Saturday, 8:30 to 9:30 p.m., Burke Lake Park's amphitheater, 7315 Ox Rd., Fairfax Station. A chance to rid yourself of some rumors with slides and information about bat diversity, behavior and adaptation. 451-9588.

BRASS RUBBING WORKSHOP -- Friday- Sunday, 9:30 to 5, Washington Cathedral, Wisconsin at Massachusetts NW, "Children's Brass Rubbing Workshop." Children of all ages can learn to produce a picture rubbing of a knight, unicorn or lion; no reservations necessary. $1.50. 364-9303.

GRIMM FOLKTALES -- Friday, 7:30; Saturday, 5:30 and 7:30; Sunday, 1:30 and 3:30, Studio A, Lisner Auditorium, 21st and H streets NW, "Grimm's Folktales in Performance." A multimedia event for children based on stories by the Brothers Grimm. $5. 387-7444.

CHILDREN'S PLAY -- Friday-Sunday, 8, Lubber Run Amphitheater, Lubber Run Park, N. Columbus and N. Second streets, Arlington, "The Magical Pied Piper." A cast of 25 children perform this classic German tale. 558-2165.

CHILDREN'S RADIO THEATER -- Saturday, 8 a.m., WPFW (89.3 FM). "The Pill that Almost Saved the World" and "Outside Looking," two radio plays by students. Listeners can participate in a call-in following each program at 783-3104.

SCAVENGER HUNT -- Friday, 8 to 9 p.m., Burke Lake Park Amphitheater, 7315 Ox Rd., Fairfax Station. Families can race the clock to find natural shapes and textures in the woods; bring flashlights. 451-9588.

CAMPFIRE FUN -- Friday, 8:45 p.m., Gulf Branch Nature Center, 3608 N. Military Rd., Arlington, "Campfire Flicks." Join a naturalist for an evening of outdoor entertainment, including nature films and a marshmallow roast. Reservations required. 558-2340.

BIRDWALKS ON ROOSEVELT ISLAND -- Saturday and Sunday, 8:30 a.m., Roosevelt Island Parking Lot, George Washington Parkway northbound. 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.

FRISBEE COMPETITION -- Saturday, 10, Burke Lake Park, 7315 Ox Rd., Fairfax Station, "1985 World Junior Frisbee Disc Contest." Kids 15 and under can compete in three events: distance and accuracy throwing and catching; winners advance to sectional and regional finals. Use your own disc or one provided by the park authority. 323-6601.

MILLSTONE GRINDING -- Saturday, 10, Pierce Mill, Beach Drive at Tilden Street NW, "The Forgotten Art of Millstone Dresser." Join a miller for a demonstration of millstone dressing; learn the techniques of grinding grain into flour and meal. 426-6829.

TROLLEY MUSEUM -- Saturday-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 PLANETARIUM -- Saturday- 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 admitted. 426-6829.

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

CHILDREN'S PLAY -- Saturday, 2 and 7, Takoma Theater, Fourth and Butternut NW, "The Land of the Dragon." A Chinese fairy tale for the entire family. Free. 576-6863.

ALL ABOARD -- Sunday, 1 to 3, Burke Lake Park, 7315 Ox Rd., Fairfax Station. Take a ride on a miniature tain; 50 cents per person. $3.50 park entrance fee for non-county residents. 451-9588.

CHILDREN'S FAIR -- Sunday, 2 to 5, the block of Heather Avenue (take New Hampshire Avenue to 410 west; go one block and make right on Elm Street; follow signs to Heather), Takoma Park, Md. Entire street blocked off for children's games, prizes, fingerprinting by Takoma Park Police Department, fire engine inspections, children's music. "Professor Video" will film your child for a small fee (VHS tape or super 8mm only); baked goods and more. 270-2619.