"What's so great about a bunch of plants, anyway?" "I hate nature." Thus do our children cheerily respond to the news that we're off to see a greenhouse.

Other families undoubtedly face visits to gardens with a sense of rollicking adventure and a song in their hearts; we go there when the children's emotions, not to mention our tempers, have crescendoed past the frazzling point. That's when we want something low- key and soothing that will bring them down to, say, the mischief level of your average plant.

The easiest place for us to get this -- and one that works even on dreary, drizzling Washington days -- is the U.S. Botanic Gardens. Its 29,000 square feet of plants-under-glass nestle at the foot of Capitol Hill, just far enough from both the halls of power and the Smihsonian to leave a few parking spaces free.

A worldwide collection -- managed under the auspices of another great Washington collector, the Library of Congress -- the Botanic Gardens are perhaps best known for their dazzling display of orchids. At least 200 of these beauties flower for the tourists each day, which is no mean trick, when you remember that orchids flower only once each year.

But our kids like to pile straight through to the palm room with its artificially created creek and hundreds of leaf-covered hiding spots, the perfect place for a game of hide and seek. And the youngest child, at three, usually wanders off to the cactus room, where the larger specimens curl around and over each other, echoing his own sense of silliness.

If we're in one of those teacherly moods parents fall into occasionally, we'll send the children off to hunt for the vanilla and coffee trees (in the subtropical room) or the pineapples (in the bromeliad room).

Or we go hunting together through the fern room for the Vessel Fern. It's easy to find -- look for its two-foot-thick stems and nine-foot- long leaf fronds. A direct ancestor of cuttings taken in 1842 from Adm. Charles Wilkes' South Seas expedition, this is probably the oldest plant in the Gardens, a spokesman says.

An expedition for us means going not to the South Seas, but to Wheaton. There, on a bright summer's day, we'll spend morning to evening doing the Wheaton Regional Park, from the Brookside Nature Center to Old McDonald's Farm.

But on a crabby, cold day, we go there to buy an afternoon's solace at Brookside Gardens -- 50 acres of beauty, including a greenhouse, run by Montgomery County.

First stop inside the greenhouse is in front of the carnivorous plants terrarium, creations whose tactical possibilities intrigue our nine- year-old ("Do you suppose they eat sisters, Mom?"). Also in that entryway are some paper puzzles, free for children to take home, and a $2 book caled the "Teacher's Guide to Trees in Brookside Gardens," with suggestions on fun ways to haul kids through the outdoors.

Inside, the plants hang and drape around several streams, waterfalls and pools, some with stone bridges that proved challenging (and therefore fun) to those under four feet tall. Right now, the greenhouse is filled with chrysanthemums, cascading plants with a luxurious number of blossoms.

"That represents a lot of love and work," says Pam Stenger, educational horticulturist with Brookside. "They're potted up in winter, moved outside in May and constantly pinched until July," she says. "Then they're tied up with nuts and bolts to make them hang right, heavily fed, continually sprayed and, while outside, fenced from the deer -- we have our problems with Mother Nature here," she says.

Stenger runs tours for school and Scout groups during the week, in which she gives them cheery assignments, like finding the "cockroach tree." That's a Ginko -- the ones with the funny, fan-shaped leaves -- which has survived life in these United States since the dinosaur era, along with a few other life forms like the cockroach.

The only other tree that can make the same claim, Stenger says, is the Dawn Redwood -- she calls it the "dinosaur tree." They got theirs from China, where it was recognized as matching fossil remains from the dinosaur era, she says. "Kids like it because they understand it -- they know what fossils are, they know who the dinosaurs were," she explains.

If you're planning to walk in the woods, one of the nicest places to head for is the National Arboretum, on 444 acres in Northeast Washington. Lots of people like to bring bikes here for an afternoon of peripatetic wandering, but if the day is too cold, or your bikers too small, you can get away with using the car.

First stop is either the Gift Shop or Administration Building for a map. The Administration Building, just off the R Street entrance, is surrounded by a moatful of Koy -- multicolored, friendly fish who bubble up to greet you. You're not supposed to feed them, but a spokesman said, "I suppose a piece of bread wouldn't hurt them."

Bringing a bagful of breadcrumbs is a good idea right now, as Canada geese and mallard ducks are making the Arboretum's ponds their temporary home. We found 30 or 40 of these waterfowl on Beech Spring Pond near the gazebo, eating bread out of a visitor's hand.

On a colder day, a good place to visit is the National Bonsai Collection, open on the Arboretum grounds from 10:30 to 2:30. This is a protected garden near the Administration Building housing more than 50 bonsai, some of which are over 300 years old. The 180-year-old Japanese Red Pine comes from the Imperial household -- the first time a bonsai from the Imperial Collection left that country.

It's not age but size that intrigued our three-year-old, looking at these miniature trees and forests. Maybe it's just fun to be taller than a tree, when you're used to being shorter than a shrub.

Across from the bonsai collection is the Arboretum's herb garden, with a wonderful water fountain -- a great place for a game of chase. Other good places to wander this time of year are the Holly Walk and Fern Valley, both of which are near parking spots.

Most people, of course, don't choose chilly days to check out these places. They pour in during spring for the bulbs and azaleas, or in summer for the waterlilies and wisteria. But we don't come to rub elbows with appreciative gardeners; we come to eject some of the gloom from these dark days.

And if we work it right -- with enough wandering, running and hide-and-seeking -- the three-year-old naps on the way back, while the older kids sit quietly with their cholorophylled fantasies. After an hour or two on earth, peace can reign. GETTING THERE

BROOKSIDE GARDENS -- 1500 Glenallan Ave., Wheaton. 949-8230. From the Beltway, take Exit 31A, Georgia Avenue, toward Wheaton. Turn right on Randolph, right again on Glenallan. The gardens are on your right. Open 9 to 5 daily except Christmas.

U.S. BOTANIC GARDENS -- First and Canal streets SW. 225-8333. Take Independence Avenue. Metered parking usually available on First Street. Open 9 to 5 daily, except Christmas.

U.S. NATIONAL ARBORETUM -- 3501 New York Ave. NE. 475-4815. Taking New York Avenue northeast past Bladensburg Road, turn right onto the service road and then to the visitor entrance. Open 8 to 5 weekdays, 10 to 5 weekends. GETTING EARTHY AT HOME

A good follow-through activity for these trips (or an alternative, if trucking kids around doesn't sound fun), is to do a little indoor gardening. If you hurry, there's enough time now to bring either narcissus or amaryllis to bloom by Christmas.

Here are directions for the Paperwhite narcissus -- a fragrant, pretty bulb available at hardware stores and greenhouses. Set the bulbs close together in a three- deep bowl (no drainhole); fill the bowl about half full with pebbles or marble chips and set the bulbs in place. Then, add more pebbles until the tops of the bulbs are just showing.

Pour water into the bowl until it touches the bulbs, and place in a cool location to allow for rooting and sprouting -- say, two weeks. Then bring the bowl to your favorite spot, and watch the plants grow and blossom. It should take about four weeks from planting to blossoming. Keep them well-watered.

Another good activity, suggests Pam Stenger of Brookside Gardens, is to send off for seed catalogues. The Gardens use a variety of catalogues; she suggests the following as reliable houses: Burpee Seed Catalogue (300 Park Ave., Warminister PA 18924); G. W. Park Seed Co. (97 Cokesburg Rd., Greenwood SC 29647); Thompson & Morgan (P.O. Box 100, Farmingdale NJ 07727).