Washington is a great place for a family vacation. The city has many wonderful facets; not the least, it has a plethora of things designed to keep youngsters interested and happy. By taking some simple preliminary steps, including interspersing the youth-oriented sites with the more sophisticated, a memorable vacation for every member of the family can virtually be assured.
First, make reservations at a hotel located as close as possible to the hub of Washington's sites. This will make it convenient to bring young children back to the room for a midday rest.
If the children are several years apart, plan that, on some days, one parent take the older child to an appropriate site while the other parent accompanies the younger child to a site pleasurable for his or her age group.
Try, too, to vary the routine. A few hours at the National Zoo (3001 Connecticut Avenue NW) or at the National Aquarium (US Department of Commerce Building, 14th Street and Constitution Avenue) can be a treat for the entire family. And so can exploring a toy shop at the unique Georgetown Park shopping mall (3222 M Street at Wisconsin Avenue NW), or at the newly restored Old Post Office (1100 Pennsylvania Avenue NW).
If parents wish to go off by themselves in the evening, bonded sitters can be provided by most hotels or by contacting such agencies as Family Care (301-588- 8200) or Child Care (202-783-8573).
What follows is a sampling of child-oriented sites in Washington and close by. Some are geared to specific age groups but all of them - the sites themselves, the surrounding exhibits or settings - are for everyone. Washington also has an almost continuous round of parades, such as the zany fun Gross National Parade along M Street on April 15, and special events such as the Smithsonian's Festival of American Folklife that features musicians, craftspeople, and performers on the National Mall (June 27 to July 1; July 4 to July 8).
Further information about sites and events, street locations, public transportation, theaters, and restaurants is available at the Washington Tourist Information Center in the Great Hall, US Department of Commerce-Herbert C. Hoover Building, 14th Street and Pennsylvania Avenue NW. Write for information to Washington Convention and Visitors Association, 1575 I Street NW, Suite 250, Washington, D.C. 20005. THE SMITHSONIAN COMPLEX
(Open seven days a week from 10 a.m. Museums are free.)
On the Mall: Uncle Beazley, a 22-foot fiberglass dinosaur is a favorite climbing spot for children. Across the Mall there are five-minute, 50-cent rides on a grand 60-animal carousel accompanied by Wurlitzer Band Organ music. (Open mid-April through Labor Day. Closed Mondays.)
National Air and Space Museum (7th Street and Independence Avenue SW): Guided tours in July and August are designed for 8- to 12-year-olds who must be accompanied by an adult.
Museum of Natural History (10th Street and Constitution Avenue NW): The Discovery Room features boxes of everything from seashells and bones to arrowheads and mammoth teeth to touch; there are spices to smell and taste, and costumes from foreign lands to try on. Ideal for toddlers and older children. (Open Mondays through Thursdays, noon to 2:30; Fridays, Saturdays, and Sundays, 10:30 a.m. to 3:30 p.m.) Sounds of North American insects fill the Insect Zoo where butterflies, cockroaches, praying mantises, crabs, and termites live in simulated environments. Children interested in watching tarantulas eat crickets or grasshoppers munch on lettuce should check the feeding schedule posted at the exhibit entrance.
National Museum of American History (14th Street and Constitution Avenue NW): A variety of exhibits promise to keep youngsters enthralled; among them, a 19 -room furnished doll house, a steam locomotive that whistles, hisses, and chugs, the turbocar that won the 1969 Indy 500, and an 1840s Conestoga covered wagon. Live demonstrations, on Saturdays, include working steam engines and other 19 th-century machines and old-fashioned printing presses on weekdays. (Check museum information desks for schedules.)
Capital Children's Museum (800 Third Street NE): A few minutes drive from the National Mall there is family fun and learning at hand that runs the gamut from a wide variety of hands-on exhibits to a communications feature where visitors can use communication devices from an Ice Age cave to a satellite earth station. (Open Tuesdays through Saturdays, 10 a.m. to 4 p.m.; Sundays, 10 to 4. Closed Mondays, $2 admission.) ROCK CREEK PARK
Rock Creek Nature Center (5200 Glover Road NW): Schoolchildren and their parents will enjoy the exhibits that tell about the park's wildlife and forest. There are also two self-guided nature walks, daily guided walks, and other ecology programs. (Open Tuesdays through Sundays, 9 a.m. to 5 p.m. Closed Mondays and holidays. Free. Reservations are needed for guided walks held on Mondays, Tuesdays, Wednesdays, 9 a.m. to 4 p.m. Call: 202-426-6829.)
Children's Planetarium (5200 Glover Road NW): Of special interest to school-agers. Present regularly featured astronomy programs about the sky over Washington. Minimum age for admission is four. (Saturdays and Sundays at 1 p.m. Free admission tickets available half-hour before show time.) IN VIRGINIA - MINUTES FROM DOWNTOWN WASHINGTON
Woodland Plantation (On US 1, 14 miles south of Washington, 3 miles from Mount Vernon): Originally part of the Mount Vernon estate, George Washington built this handsome home as a wedding gift for his foster daughter, Nelly Custis. Now a property of the National Trust for Historic Preservation, the mansion appears as it did in the early 1800s with a special ''touch and feel'' room for youngsters. The grounds include nature trails and formal gardens. (Open daily, 9:30 a.m. to 4:30 p.m. Closed Thanksgiving, Christmas, New Year's. Admission fee.)
Theodore Roosevelt Island (On the Potomac River, 10-minute drive from downtown Washington. Access is via footbridge from Roslyn; just north of the Theodore Roosevelt Bridge on the George Washington Parkway in Virginia): An 88 -acre wilderness preserve featuring 11/2-hour guided nature walks for adults and children eight years of age and older. Guides point out and describe the island's edible plants, wildflowers, animal habitats. There is also an imposing statue of Theodore Roosevelt. (Call 703-285-2598 to reserve for Monday, Tuesday, or Wednesday guided walks. Weekend walks are scheduled for 2 p.m. on Saturdays and Sundays. Free.)
The Claude Moore Colonial Farm at Turkey Run (Approximately 12 miles from Washington. George Washington Memorial Parkway north to exit for Route 123 to McLean. Drive almost 1 mile, bear right on Route 193, make first right at farm sign): Living farm reproduces life on a small-scale, low-income homestead in northern Virginia during the late colonial days. The 100 acres are worked by the ''farmers'' with crops, gardens, and orchard. Livestock roam freely. Meals are prepared over an open hearth with food raised on the farm. From April through September, ''Evenings in 18th Century Rural Virginia'' feature period music, country dancing, and other colonial leisure activities. (Open 10 a.m. to 4:30 p.m. Wednesdays through Sundays from April through November; Friday through Sunday from December through March. Call 703-442-7557 for ''Evenings'' performance information. Free.)