Did the camel walk a mile for his hump? Nova Scotia's Mermaid Theater uses masks and puppets to give you the answer (along with an explanation of how the elephant got his trunk), in a presentation of Rudyard Kipling's "Just So Stories," which runs through June 7 at Discovery Theater.

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. 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, 11 to 2, "Corn Planting," watch farmers plant corn. Sunday, 8 a.m., bird walk, wear walking shoes and bring binoculars. 839-1177.

DISCOVERY THEATER -- Tuesday through 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. $2.50, discounts for families and groups. 357-1500.

CAPITAL CHILDREN'S MUSEUM -- Daily, 10 to 5, 800 Third St. NE. Saturday and Sunday, museum hours, "A Special Present for Mom," use the museum printing press to make a Mother's Day card. Museum admission, $2; mothers free on Sunday. 543- 8600.

NATIONAL COLONIAL FARM -- Tuesday through Sunday, 10 to 5, 3400 Bryan Point Rd., Accokeek. Sunday, 1 to 4, "From Sheep to Shawl," watch sheep shearing, spinning and knitting of wool. 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, "Crash the Clown," juggling, acrobatic and music. Adults, $2 donation. 301/823-2551.

CHILDREN'S RADIO THEATER -- Saturday, 8 a.m., WPFW 89.3 FM. "The Revolt of the Insomniacs," for kids who hate to sleep. Listeners can participate in a call-in following each program by calling 783-3104.

CRAFTS FAIR -- Saturday, 9 to 4, Eastern Market (North end), Seventh and North Carolina Avenue SE. The 9th annual Capitol Hill Day School crafts fair features more than 40 craftspeople selling everything from antique mirrors, stained glass, jewelry to appliqued children's clothing. There's also a children's corner for secondhand toys and books, plus a bake sale, charcoal-grilled sausages and beer for sale. 543-2497.

SATURDAY MORNING AT THE NATIONAL -- Saturday, 9:30 and 11, Helen Hayes Gallery, National Theater. "Clown Conspiracy," Olaf and Zerphrelli combine pantomime and gibberish. Reservations recommended. 783-3372, 24 hours a day.

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.

KIDS' CARNIVAL -- Saturday, 10 to 4, Prince George's Plaza Community Center, 6600 Adelphi Rd., Hyattsville. Games, rides, palm reading and crafts. 864-1611.

FUN FAIR -- Saturday, 10 to 3, Green Hedges School, 415 Windover Ave., Vienna. Moon bounce, cake walk, pony rides, haunted house, gold fish, cabbage patch doll clothes and prizes. 938-8323.

SOAP BOX DERBY WORKSHOP -- Saturday, 10 to noon (ages 9-12); 1 to 3 (ages 11-15), Washington Gas Light Company, 6801 Industrial Rd., Springfield. Learn how to build a soap box racer and official racing rules and tips. 653-5060 or 229-0118.

MAY FAIR -- Saturday, 10 to 3, Robert Frost Elementary School, 6419 85th Ave., New Carrollton. Arts and crafts, pony rides, entertainment, games and more. 552-3400.

FUN FAIR AND FLEA MARKET -- Saturday, 10 to 3, St. John's Church, 9801 Livingston Rd., Fort Washington, Md., "Broad Creek Country Day School's 6th Annual Fun Fair," pony rides, face painting, games. 292-1406.

MAY FAIR -- Saturday, 11 to 3, Pine Crest Elementary School, 201 Woodmoor Dr., Silver Spring. Games, prizes, raffle, white elephant, face painting. 593-1784.

THE OLD POST OFFICE -- Saturday, 11:30, Old Post Office, Pavilion, Main Stage, 1100 Pennsylvania Ave. "The Town Clowns" perform zany magic and mime. 289-4224.

MAY FAIR -- Saturday, noon to 4, Highland Elementary School, 3100 Medway St., Silver Spring. Raffle, pony rides, balloons, games, plants, spin art. 946-4826.

TAYLOR SCHOOL FUN FAIR -- Saturday, 11 to 3, 2600 N. Stuart St., Arlington (off Military Road). Games, moon bounce, crafts, country store and more. 243-1094.

ARTS AND FUN FAIR -- Saturday, 11 to 3, The Lab School of Washington, 4759 Reservoir Rd. NW. Art show, moon bounce, treasure hunt, silent auction for autographed cartoons and more. 965-6600, ext. 14.

ARTS FAIR AND COUNTRY MARKET -- Saturday, 12 to 5, 16923 Norwood Rd., Sandy Spring, Md. (off Route 108). Petting zoo, silent auction, face painting, dunking booth, archery shoot. 301/774-7455.

FIESTA -- Saturday, noon to 5, Oyster Bilingual School, 29th and Calvert streets NW, /nnual fiesta, raffle, entertainment and Spanish food. 659-6532.

CHILDREN'S THEATER -- Saturday, 7:30, Mount Calvary School, 6704 Marlboro Pike, Forestville, Md. The Mount Calvary Drama Club presents "The King and I." $2.50 adults; students and seniors $1.50. 735-5262.

MOTHERS DAY MAYFEST -- Sunday, noon to 3, Green Spring Park Horticulture Center, 4603 Green Spring Rd., Annandale (take Beltway Exit 6-E, Little River Turnpike, east three miles; make left at Green Spring Road; Horticulture Center on right). "Third Annual Mothers Day Garden Party," listen to a German oompah band, browse over plants and crafts; games for children (mothers receive a free plant). 642-5173.