SOME KIDS KNOW WHAT THEY want to be when they grow up before they grow up. A few kids know that what they want is to run a company, and they already do. Marketing their own ideas, starting their own businesses -- and making money -- they are CEOs still in their teens.

Successful in adult terms, but kids nevertheless, these young entrepreneurs live in a curious, half-grown-up world. They still live at home and have to remember to check in for dinner -- but they also plan inventories, hire personnel, worry about expansion and take risks.

Despite their financial success, it is on the grown-up side of money issues that many of them show how young they still are. Money has often come in too fast for them to grasp all its implications.

"Taxes?" asks the usually articulate artist Grace Jeffers. "Gee, I don't know about taxes."

What she doesn't know about her tax situation she will soon learn -- most likely from her businessman father. Like the others, Jeffers comes from an uncommonly close family that backs her ambitions and helps her when needed.

The gifts of most of these teen-agers were recognized and encouraged from an early age. Jeffers began studying art at 4. Lisa Wessel- McIntyre, a dancer, showed promise and was given lessons at 3. Computer expert David Stern, his mother says, tried to figure out how his toys worked before he could crawl.

Grace Jeffers, mother of the artist, speaks of her talented daughter this way: "I see her future as a very bright future. I admire her. I mean, don't you?"

Of his gardener son, surgeon Paul Shorb says, "Gardening is a field I don't know anything about, and I always sort of marvel at people who succeed at business of any kind. Basically I approve of (what) John's doing . . . that he's doing it on his own."

WHEN JOHN SHORB opens the door of his Spring Valley family home, he's wearing a pair of jeans worthy of a seasoned ranch hand and a green T-shirt announcing his business, Northwest Lawn Service. A discreet earring gar his toes sprout through the holes of socks so far gone they wouldn't qualify for most ragbags.

The youngest of five children, he is an outdoorsman among intellectuals, a redhead in a family of blonds and brunets, a conservative in a nest of liberals. He has been in the gardening business for nearly half his life.

In the six months since he graduated from St. Albans School, he has grossed about $60,000. He owns one Datsun truck, one Bobcat cutting machine, an assortment of blowers, mowers and trimmers and hires at least two full-time employes, depending on the season. He also does his own books, billing and, until this year, his own taxes.

His profits are mainly tied up in capital investments, and when an expert went ove his books he learned the unhappy news that he probably owes the IRS more than he had thought. Asked how much, Shorb hesitates. "Let's just say the 25-

Shorb found his vocation early. In fifth and sixth grades, he was cutting lawns. Learning from his mother, herself an expert landscaper, and from other customers, he began to branch out into trimming, weeding and seeding. "By seventh grade," Shorb says, "I knew I'd rather be outside working than watching TV or doing homework." His grades, he admits were "mediocre . . . well, below mediocre."

By ninth grade he knew every plant that grows in the Washington area. Mornings, he rose early to work before classes; afternoons, he won rarely granted dispensation from sports so he could get to the lawns and shrubs needing his attention. Summers, while other family members traveled or visited the family vacation home in Maine, John Shorb stayed home to cultivate. He never felt he'd missed out. "By the end of the day, you know you've done something . . . then you go by and look at what you've done, and it's beautiful."

Bouncing in his Datsun pickup through the neighborhood of exquisitely tended grounds, many of them his handiwork, Shorb stops at customer Barry Wood's house to look over a back yard he helped renovate last summer. He and Wood consider empty spaces where old shrubs and trees used to be and admire the young redbuds, rhododendrons and magnolias that promise splendid springs to come. Shorb bends low over a baby boxwood and clucks paternally: "Not doing well."

Back in the truck, he speaks about the difficulties of good customer relations. Wood and his wife, Shel, for example, were displeased with the lawn he had guaranteed would grow despite shade, and they threatened to sue him for $500. Shorb did some replanting and replacements and worked hard to smooth things out. "I really want my customers to be satisfied," he says, then adds stoically that tough customers at this stage teach him a lot.

Shorb has decided to delay college to get a good sense of the needs of his business cycle. In a year or two he intends to go to a local college -- perhaps the University of Maryland or G.W.U. -- for a double major in business and landscaping. Eventually, when he has about a dozen employes to run things, he plans to go away to get a master's degree in landscape design. In 10 years, he estimates, his will be the major horticulture center in the Washington area. From there, he will just continue to expand. "If I like it," he adds emphatically.

"And if you don't?" his visitor asks hesitantly.

Unable to imagine not liking it, he smiles and for once has nothing to say.

"I THOUGHT I'd have to pay taxes in eighth grade," says David Stern, 15. "I felt kind of proud." In fact, until a recent check of his computerized accounts, he thought he had paid taxes that year. As it turns out, he escaped Uncle Sam's long reach then, although he's definitely on the tax rolls now.

The slight 10th-grader at Woodward High School sits in his basement office at his Rockville home and explains the confusing array of computer hardware, disk drives, monitors and printers. In his crew-neck sweater and Docksiders, he looks every bit the high school student that he is, and very little like the president of the Design Soft software computer education and consulting company, which he also is.

Pointing out a now old-fashioned Apple II computer, he says, "My parents gave this to me just for fun in sixth grade," says Stern, " . . .I sat down with it and couldn't take my hands off it." Bit by bit the system grew until it dominated what once was his father's study.

"David turned the whole family on with computers," says his mother. Rosalind Stern learned enough from her son to become director of computer education at McLean School in Potomac, where she teaches second and third grade. Now she is working on an MA in computer education and training.

David also helped his father to learn word processing. Stephen Stern then went on to other skills that he now uses in his work as a government engineer and as a professor of business administration. Even David's 12- year-old sister, who likes to write, now has her own computer in her room.

David taught himself how to use his Apple and by eighth grade had become so proficient in the BASIC language that he was asked to teach other students in his school. Soon he was also teaching usage and programming in another junior high and at Bethesda Computers, earning at least $100 a week. He began to attend the Apple Pi users group sessions to exchange information with other Apple buffs.

From an eighth-grader's point of view, there was something wrong with the Apple Pi meetings: many kids attended, but nothing was geared to their interests. Stern organized the kids into their own splinter group, named it Apple Seeds, and was elected its first president. Soon there were more than 50 members who met to exchange programs and form a kid-oriented library.

Stern then began writing and editing the "Apple Seeds Corner" in the organization's newsletter, Washington Apple Pi Journal. Among his articles were one titled "Parabola" based on an equation given by his math teacher, a review of games with names like Gorf, Centipede and Pleiades, and how-to tips on hooking your computer up to your stereo.

"Hooking your computer up to your stereo?"

"Oh, yes," Stern answers patiently, "It's to amplify the sound of the games."

Stern's success with the Apple Seeds drew the attention of the international organization of Apple users, which elected him to head its "worldwide family interest group."

By ninth grade, Stern's computer activities had grown so diverse that he felt he should start his own software and consulting company. His first major program, Mastershell, which he wrote with his mother, teaches teachers how to write educational programs. He's now searching for a publisher and hopes to earn $12- -- the price, he says wistfully, of a Pontiac Fiero.

Stern already looks beyond school to the time when he can really be on his own. "I've always hated that teachers don't want you to do what you want . . . Maybe I'm rebellious, but I don't want to do things to exact standards. I like to do things my own way."

The 15-year-old dislikes feeling dependent, and worries that with adulthood he may have to make a painful choice "between security and freedom."

What does the choice mean to him?

Stern lights up. "Security is driving a Dodge. Freedom is having a Pontiac Fiero."

IT IS DIFFICULT to document just how widespread this youthful affection for business is, but according to Elaine Saunders, senior program manager for Junior Achievement Inc., it is definitely a growing trend. Junior Achievement, which stresses partnership between businesses and youth, enrolled 3,000 students in the Washington area alone last year, and 4,000 more were turned away for lack of business sponsorship.

In Saunders' opinion, youthful enthusiasm for free enterprise reflects an increasingly conservative mood among kids at all levels. "Young people today," says Saunders, "know they need to look out for themselves. They feel they cannot depend on others -- especially on the government, nor the welfare system -- to do for them what they can better do for themselves."

Dancer, model and actress Lisa Wessel-McIntyre, 1, not only acquired an enthusiasm for free enterprise for herself; she also went on last year, her senior year at Alexandria's T. C. Williams High School, to imbue others with it. It was all part of her assignment to head the school's annual free enterprise project sponsored by Phillips Petroleum, which was given to her after her essay "What Free Enterprise Means to Me" was judged the school's best.

"I like to compete," says Wessel- McIntyre. "And I like to win."

In the project Wessel-McIntyre was charged with "informing a group in the community about free enterprise." She decided to teach about the profit margin; for her community group she picked all 750 of Alexandria's public school fourth-graders.

Bussing them to T. C. Williams over a period of four days, she taught theory first. Using slides and an overhead projector, she outlined the basics of buying and selling apples for a profit. Then came practical experience. Divided into groups of 10, the children were given a bag of lemonade packs (donated by Wyler Foods), cups (donated by McDonald's Corp.) and a change-making chart. After a pep talk on customer relations, the budding capitalists were sent out to sell.

But these days the capitalist spirit is not only nurtured by such formal programs. It seems to show up wherever kids do what kids do.

On a Saturday afternoon in early winter, a Glover Park row house seems to lift off its foundations. In the jumbled basement bass guitarist Stuart Hill, 16, a junior at Gonzaga high school, practices with his band, Stuge.

Hill, together with singer Bobby Jones, a senior at Maret School, runs DCene, a miscellany of underground rock activities they describe as "a big Pentagon of things." Using savings from a paper route, the two invested in a lot of black T-shirts on which they silk-screened the album cover art of the popular local band Government Issue. They got permission from the band to sell the shirts at a concert -- and sold out. They then sold stickers for Minor Threat, another local band; published a magazine, also called DCene ("a public service"), that reviewed concerts, albums and new groups; and returned to T-shirts. Their second design, which includes skulls, a cross and knives, is currently sold at a Georgetown shop called Smash. Stuge itself has just cut a record and will appear Feb. 1 at the Chevy Chase Community Center.

The profits from one project are put back into a general pot to fund the next. The point of DCene is just to keep itself going. "Free enterprise is basically good because we can do what we want," says Jones. "Obscene profit is not good," qualifies Hill.

The two aren't sure what their own profit is, but most likely it isn't obscene. They considered opening a bank account once, but decided against it when they realized it would require a $50 minimum balance.

SITTING IN FRONT of the window of the City Paper office, where she works as an intern, Grace Jeffers, 17, twists her long body as though in search of expression. Her outfit is striking, especially the T-shirt -- which is her own creation.

"Other people see the design. What I see is my heart imprinted," she says. The "heart imprinted" is a stylized female face made from a stencil and printed all over the shirt.

T-shirts are only part of the line of hand-painted clothing the Madeira School senior has developed. She also makes dresses, scarfs, mufflers and shoes that all carry the distinctive face. Her T-shirts usually sell for $25 to $30, and her dresses average between $240 to $350, although custom items go for as much as $750.

Influenced by an artist named Grace de Lacey, who painted women (and is, Jeffers later admits, her mother), Jeffers says the face evolved as she herself developed as an artist. Once she had perfected the face, she trademarked the stencil. "It's my status symbol," she says.

"What I do is wearable art," she says. "I use the human body as a stretcher." In 11th grade, when she became a boarding student at Madeira School in Greenway, she had her first sales -- her designs sold out at the school Christmas bazaar.

Since she had her own studio and painted three or four hours a day anyway, she raised her sights. Buying wholesale bolts of cotton, T-shirts on sale at K mart and silk at a discount from Apparel Mart in Chicago, Jeffers hired four Chicago seamstresses part-time to sew the cloth she painted.

Chicago and Georgetown boutiques started buying her creations. Now she's negotiating with JC Penney and Neiman-Marcus to sell entire lines. Lately she has been grossing about $1,200 a month, but if negotiations go well, she says, she may soon get a very big order -- perhaps $30,000.

"I'm an overachiever in my own eyes," she says. She has applied to Harvard for early admission. She loves music and writes poetry. At school she edits both the literary magazine and the school paper. It was a love of writing that brought her to City Paper. She's in charge of exhibitions for art shows and began the forensics team at Madeira, which she also coaches. "I feel speaking is important," she says.

She used to be a disc jockey for a college radio station. "Did I tell you?" she asks. "Sometimes I'm a go-go dancer -- with all my clothes on -- for the Fleshtones."

One more thing. She loves going home -- even if she does have to become a debutante ("They say it's inevitable") and loves her family.

She pauses, poised to answer a question not yet asked, a question about the future.

"If I go to Harvard next year . . . ," she begins. Of course, there will be difficult choices. Perhaps she will decide to study English or art. Or just maybe she'll opt for business. No matter what, she's committed to keeping her business going now. "It's part of my future, definitely part of my life."