Take advantage of this unusually cool summer with a tromp through the woods this weekend. On Saturday at Prince William Forest Park near Quantico, kids six to 12 can take a nature hike with a ranger who'll teach about wilderness safety, conservation, wildlife and how to read those happy trails. If you're quiet and lucky, you may even come across wild animals. An hour before this walk, you can watch a snake feeding demonstration at the park's nature center.

Sunday, the rough 'n' ready can hit the beaten path for a solid two- hour, four-mile hike with a naturalist in Rock Creek Park, beginning at the Boundary Bridge at the District- Maryland line. Wear sturdy shoes and long pants.

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 (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 and Sunday, 11 to 3, "Wheat Threshing." Take in the sights and sounds of a turn-of-the-century threshing operation. 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. 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. Saturday and Sunday, "Celebrate America's Birthday." Make a special Independence Day print on the museum's printing press. Museum admission, $2. 543-8600. DOLL'S HOUSE & TOY MUSEUM

Tuesday through Saturday, 10 to 5; Sunday, noon to 5, 5236 44th St. NW. 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, 2, "Pressed Flower Demonstration." Learn how to press and preserve flowers; reservations necessary. 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, museum hours, "Wood Sculpture: Wacky Wonderful Art." Work with wood scraps, toothpicks and glue to make your own sculpture. $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 prior to the Revolutionary War. 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 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. BRASS RUBBING WORKSHOP

Friday- Saturday, 9:30 to 5, Washington Cathedral, Wisconsin and Massachusetts avenues 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. CHILDREN'S PLAY

Friday-Sunday, 8 p.m., Lubber Run Amphitheater, Lubber Run Park, N. Columbus and N. Second streets, Arlington, "The Magical 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. "Big Anthony and the Magic Ring" and "Helga's Dowry: A Troll Love Story," two stories by Tomie de Paola. Listeners can participate in a call-in following each program by calling 783-3104. TBIRDWALKS 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 baseball pitching machine; bats, balls and helmets provided. $1 for 20 balls; team reservations. 301/248- 4404. CHILDREN'S OPERA

Saturday, 11, Wolf Trap Farm Park for the Performing Arts, 1624 Trap Road, Vienna, Va. (take Rte. 7 west from the Capital Beltway for 21/2 miles and turn left at Towlston Road, at the brown Wolf Trap directional sign), "Fluerette." A special one-act opera for children based on Offenbach's comic operetta. Free, but advance reservations necessary. 255-1827. TROLLEY MUSEUM

Saturday and Sunday, noon to 5, 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. PRINCE WILLIAM FOREST PARK

Saturday, 2, Nature Center, near Quantico, Va. (take I-95 to Rte. 619 west; park entrance 1/2 mile on right, follow signs to nature center), "Snake Feeding Demonstration." See a king snake, black rat snake and mole snake feed on live prey; 3 to 4, "Children's Hour," kids six to 12 can join a ranger for a nature walk to learn about forest conservation, how to read trails and more. 703/221-2104. CHILDREN'S NATURE HIKE

Sunday, 10 a.m., Boundary Bridge on Beach Drive, Rock Creek Park, District-Maryland line (take Connecticut Avenue to East-West Highway traveling east; make right on Beach Drive, follow until road ends at parking lot. Meet ranger there), "Limber Up." Join a park naturalist for a two-hour, four-mile hike through the woods; wear sturdy shoes and long pants. 426-6908.