Maryland will be rocking this Friday with some back-to-school fun. A rollerskating/pizza party in Hyattsville will keep the kids spinning and rolling as DJs Doc Reeber and the Bean play the hottest new sounds. And the latest dance tunes will be unleashed in Seat Pleasant at a dance for pre- teens and elementary school children. Parents are also welcome to try and outdance the kids.

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). Sunday 9:45 a.m., join the farmer on a tractor-drawn wagon ride; meet in the barnyard. 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 to 4, Rose Hill Children's Museum, north of Frederick. 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. $2; special performances an additional $2. Sunday 11:30 and 12:30, listen to Kay White tell funny stories and sing funny songs; audience participation welcome. 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. Adults $1; children under 12, free. Sunday 1 and 3, toast the bride an groom with apple cider as the staff recreates a farm wedding; wedding feast and gifts on display. 301/283-2113.

CLOISTERS CHILDREN'S MUSEUM -- Wednesday through Friday, 10 to 4:30; Saturday, 12 to 4, 10440 Falls Rd., Brooklandville, Md., "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.

BACK-TO-SCHOOL DISCO -- Friday, 7 p.m. to 10 p.m., Seat Pleasant Activities Center, 5720 Addison Rd., Seat Pleasant, Md. Pre- teens can bop and spin to the newest sounds around; free hot dogs to the first 50 arrivals. Kids, $2; parents free. 773-6685

SPIN-A-DRUM -- Friday and Saturday, 10 to 5, Takoma Hardware and Paint, 6909 Laurel Ave., Takoma Park. Kids can spin-paint a picture; popcorn and balloons also. Reservations suggested. 270-0055.

CHILDREN'S RADIO THEATER -- Saturday, 8 a.m., WPFW 89.3 FM. "The Galaxy Girls and the Case of the Great Liberty Larceny" and "Cosmic Kid and the Case of Someone's Been Tasting My Porridge." Two outer space mysteries. 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. Kids help the Prince George's Civic Opera Company act out the fairy tale opera "Hansel and Gretel." Reservations recommended. Call 783-3372, 24 hours a day.

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.

STORYTELLING -- Saturday, 12:30 p.m., National Museum of African Art, 318 A St. NE, "Storytelling: Igbo Folktales." Experienced storytellers recount lore and history of the Igbo people of southeastern Nigeria. 357-2700.

ROLLERSKATING AND PIZZA PARTY -- Saturday, 7 p.m. to 10 p.m., Prince George's Plaza Community Center, 6600 Adelphi Rd., Hyattsville (take Beltway to the New Hampshire exit, left on Adelphi Road and the plaza is six miles on the right). Music, pizza and rollerskating for kids ages six and up. $3.50 includes admission, skate rental, pizza and drink. 864-1611.

WILDLIFE EXCURSION -- Saturday, 10 to 11, Royal Lake Park, 5344 Gainsborough Dr., Fairfax. (Take Beltway exit 5-W Braddock Road west to left on Twinbrook Road to right on Commonwealth to left on Gainsborough to the park entrance on left). Join a naturalist on a search for beaver and other waterfowl; nature awareness games also part of the fun. 941-5000.

FAMILY PLAY DAY -- Saturday, 11 to 4, the Mall (between Eighth and 10th streets NW). Celebrate the accomplishments of the disabled with a variety of fun and educational activities, including a football game with former Redskin wide receiver Roy Jefferson. 393-1250.

FAMILY WETLAND LAB -- Saturday and Sunday, noon to 5, Huntley Meadows Park, Harrison Lane, Fairfax. Take the Beltway to exit 1-S (Richmond Highway, Route 1) south 3.5 miles to a right at Lockheed Boulevard, go three blocks to the park entrance on the left at Harrison Lane). Collect your own wetland water samples for investigation under microscopes. 768-2525.

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 Stone That Sings." A play in which the audience makes 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 Park Nature Center, 2845 Marcey Rd., off Military Road, Arlington. Naturalists tell stories for pre-schoolers and kindergarteners. 528-5406.

CHILDREN'S DAY -- Sunday, noon to 4:45, Ladew Topiary Gardens, 3535 Jarrettsville Pike, Monkton, Md. Enjoy 22 acres of beautiful gardens as well as clowns, storytellers, plays and a treasure hunt. Adults $2.50; seniors $2; students over 12, 50 cents.

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.