For those of you who yell, "Don't do it!" in the middle of movies, your golden opportunity to control the fate of fictional characters awaits at Adventure Theater.

It's presenting "The Stone That Sings," a choose-your-own-ending play about knights, maidens, dragons and the search for a magic stone and pearls of wisdom. The plot gives way to audience responses, which shape one of eight possible endings. "The Stone that Sings" runs through September 22.

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, 9:45 a.m., "Good Morning Hayride." Take a 45-minute tractor-drawn hayride through the farm's lower acreage and along the riverside; meet at the barnyard. Reservations necessary. Sunday, 9 a.m., "Farmer's Photo Walk." Beginning shutterbugs can take a walk through the farm and snap away; also learn tips to improve your photos. Meet in parking area. 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. 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.

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.

CAPITAL CHILDREN'S MUSEUM -- Daily, 10 to 5, 800 Third St. NE. Friday, 10:30; Saturday, 11, "Puppets on Parade." A variety show of colorful hand, rod and mouth puppets performing musical numbers. Museum admission, $2; special performances an additional $2. 543-8600.

DOLL'S HOUSE AND 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-

NATIONAL COLONIAL FARM -- Tuesday through Sunday, 10 to 5, 3400 Bryan Point Rd., Accokeek, "Colonial Confections." See farm staff prepare colonial sweets. 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, "Indian Summer Celebration." Hunt bear and porcupine hidden along a nature trail, dance around a totem pole and see an extensive Kachina doll exhibit. Saturday, museum hours, "Indian Crafts": make tepees, sandpaintings and decorate Indian headbands. $2 donation requested from adults; group tours available. 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. 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.

WOLF TRAP -- Friday, 10 to 1, Wolf Trap Performing Arts Center, 1551 Trap Rd., Vienna. "Theater in the Woods." Contemporary dance, American folk music and children's theater. Programs free, but call for reservations and schedule. 255-1827.

NATURALIST CORNER -- Friday, 1 to 4, Hidden Oaks Nature Center, Annandale Community Park, 4030 Hummer Rd., Annandale, (take Beltway Exit 6-E, Rte. 236 east; make left at first light at Hummer Road. Park entrance on right). Spend an afternoon exploring nature through reading and art. 941-1065.

CHILDREN'S RADIO THEATER -- Saturday, 8 a.m., WPFW 89.3 FM. "More Tales of Br'er Rabbit," a story about more backwoods mischief from Br'er Rabbit and his friends. Listeners can participate in a call-in following each program by calling 783-3104.

INSECT TREK -- Saturday, 10 to 11:30, Rock Creek Nature Center, 5200 Glover Rd. NW. Take a stroll with a naturalist in search of the area's six-legged creatures; appropriate clothing adivised. 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 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. "A Stone That Sings." A story in which the audience must make decisions to affect the outcome. $3, group rates available. 320-5331 weekdays and performance days from 10 to 2.

CHILDREN'S STORY HOUR -- Friday, 3 to 4, Potomac Overlook Regional Park Nature Center, 2845 Marcey Rd., off Military Road, Arlington. Naturalists tell stories for pre- schoolers and kindergarteners. 528-5406.

BUTTER FINGERS -- Saturday, 10 a.m. to noon, Ellanor C. Lawrence Park, Walney Visitor Center, Walney Road, Centreville, Va. (I-66 west 11 miles to left on Rte. 28; go one- tenth of a mile and make a right on Walney Road. Visitor Center lies one mile on left.), "For Butter or Worse." Watch a Holstein get milked for all it's worth, then help with the churning to make butter. 631-0013.

FESTIVAL FOR CHILDREN -- Saturday, 10 to 4, Courthouse Square Park, Rockville (take Beltway to Rte. 355 north to Rte. 28 west; park is at intersection of Rte. 28 and Maryland Avenue), "Children's Festival." A crafts fair tailored especially for kids; the day includes facepainting, toys, dolls, children's music and more. 424-8000, ext. 337.

FAMILY DAY FESTIVAL -- Saturday, 11 to 9:30, Fort Circle Park, 12th and Galloway streets NE, "12th Annual Upper Northeast Family Day Festival." A day of pony rides, moon walks, karate, music and more; picnics welcome. 476-6863 or 529-1579.

OLD POST OFFICE -- Saturday, noon, The Pavilion, 1100 Pennsylvania Ave. NW. The Town Clowns return for more fun and games. 289-4224.

MUSIC FOR THE INNER CITY -- Saturday, 5, Barry Farms Recreation Area, Suitland and Firth Sterling roads SE, "Second Annual Music for the Inner City Program." The sixth of eight summer concerts designed to introduce children to classical music and the instruments themselves. Eight musicians will be on hand to perform and answer questions from the audience. For directions and more information, call 699-5440 or 699-0440.

THEATER FEST -- Sunday, noon to 6, Glen Echo Park, Glen Echo. A day full of mime, dance, reader's theater, workshops and other family programs. 492-6282.

BELGIAN CHOIR -- Sunday, 3, All Saints Episcopal Church, 3 Chevy Chase Circle, Chevy Chase. "Les Pastoureaux." The acclaimed youth choir from Waterloo, Belgium performs Schubert's "Mass in G Major," as well as folk and popular music. 654-2488.