Wolf Trap opens its fall children's season Saturday with folk music from local musicians Cathy Fink and Marcey Marxer. The folks at Wolf Trap have something planned every Saturday this month, including an instrument-making workshop, a pantomime, a storyteller and "Dinosaur Rock."

Arlington's Thomas Jefferson Center also has its November calendar full of free Saturday drop-in activities for children six to 12. This weekend you can spend an afternoon rollerskating; skates and supervision provided.

If the possible panda pregnancy has you on your way to the the National Zoo this weekend, please bear in mind the panda lair is closed and that winter hours are now in effect.

The following events are free unless otherwise noted.

CAPITAL CHILDREN'S MUSEUM -- Daily, 10 to 5, 800 Third Street NE. Friday, 10:15; Saturday and Sunday, 1 and 2:30, "Hansel and Gretel." A one-man puppet production adapted from Humperdinck's children's opera. Saturday and Sunday, museum hours, use ink, per and leaves to make your own leaf print. $2 museum admission; special performances an additional $2.50. 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- 0024.

NATIONAL COLONIAL FARM -- Tuesday through Sunday, 10 to 5, 3400 Bryan Point Rd., Accokeek. Sunday, 1 to 4, make soap the traditional way using wood ashes and animal fat. Admission: Adults $1; children under 12, free. 301/283-2113.

DISCOVERY THEATER -- Tuesday-Friday, 10 and 11:30 a.m.; Saturday, 1 and 3, Discovery Theater, Arts and Industries Building, 900 Jefferson Dr. SW. Classic Stories, Enduring Tales: "The Ugly Duckling." A puppet-production of the Hans Christian Andersen tale; recommended for pre-kindergarteners through third grade. Adults $3; 12 and under,$2.50; group rates available. For more information and reservations, call 357-1500.

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, will round out this history lesson. Adults $1; children under 12, 50 cents. 703/442-7557.

BOOK AND TOY FAIR -- Saturday, 10 to 2, St. Margaret's Episcopal Church, 1820 Connecticut Ave. NW. A wide variety of children's books, toys and clothing. 234-6664.

KENNEDY CENTER -- Saturday, 10:30 a.m. and 12:30 p.m.; Theater Lab, John F. Kennedy Center for the Performing Arts, "Lady Liberty." A musical written especially for the Kennedy Center to celebrate the centennial of the Statue of Liberty. The story is about a young immigrant living in the United States and is recommended for children ages seven through 13. 254-3600.

CHILDREN'S RADIO THEATER -- Saturday, 8 a.m., WPFW 89.3 FM. "Monsieur Vendome," a story by a mother-and-daughter writing team. Listeners can participate in a call-in following each program by calling 783- 3104.

SATURDAY MORNING AT THE NATIONAL -- Saturday, 9:30 and 11, Helen Hayes Gallery, National Theater. Jean Ross performs finger plays, silly poems and songs for children. Reservations recommended. Call 783-3372, 24 hours a day.

DISCOVER THE GALLERY -- Saturday, 10 to 11:30, National Gallery of Art, 4th and Constitution Avenue NW, "Objects Fit for a King." A program for families with children ages six to 12. Docents from the Folger Library will dress a child from the audience in English Renaissance costume and describe it. Then take a museum tour of decorative arts and furniture from the Renaissance. Free, but advance registration required. 842-6249.

FALL FUN FESTIVAL -- Saturday, 10 to 8, St. Ann's Church, 980 N. Frederick, Arlington. Games, toys, rummage sale, baked goods, books. 528-6276.

SATURDAY FILMS -- Saturday, 10:30, Alexandria Library, 717 Queen St., Alexandria. Three films for young children: "Millions of Cats," "The Pumpkin Who Couldn't Smile" and "Tenny-Tiny and the Witches." 838-4555.

WOLF TRAP -- Saturday, 11 and 1, The Barns, 1624 Trap Rd., Vienna. Cathy Fink and Marcy Marxer perform folk music in this special children's program. $4. 938-2404.

FALL CARNIVAL -- Saturday, 11 to 3, Barcroft Elementary School, 625 South Wakefield St., Arlington. Moonbounce, games, food, old-fashioned cakewalks, toys, crafts and treasures. 920-6423.

OLD POST OFFICE -- Saturday, noon to 1, Pavilion, 1100 Pennsylvania Ave. NW. The Town Clowns perform live on stage. 289- 4224.

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. "The Magic Flute," a one-hour marionette version of the Mozart opera, featuring dragons, flying horses and enchanters. $4, group rates available. 320-5331 weekdays and performance days from 10 to 2.

LIBRARY BIRTHDAY PARTY -- Saturday, 2 to 3:30, Georgetown Library, Wisconsin and R Street NW. The Town Clowns, balloons, face-painting, skit, refreshments. 337-5753.

BLUE SKY PUPPETS -- Sunday, 2, Rock Creek Nature Center, 5200 Glover Rd. NW, "Lights Out on the Bunny Brothers." A 45- minute presentation featuring singalong, music, puppet show and other entertainment relying on audience participation. 426-6829.