When Vanessa Wauchope was growing up in Westport, Connecticut, she spent her free time doing what many teenage girls did for pocket money: She babysat.

For $2.50 an hour, she was a mother's helper, accompanying women from her church as they went to the beach with their children. In high school, she schlepped neighborhood kids around their seaside town in an S.U.V. and went along on family road trips to Nantucket and Martha's Vineyard.

In college, Wauchope studied business and figured her babysitting days were behind her. But when a family tragedy prompted her to move to Manhattan at age 21, she began babysitting again for extra money. She soon found herself with more work than she could handle from worldly, well-to-do parents who were utterly desperate for flexible, part-time child care.

"It got to the point where I had too many clients," says Wauchope. "I began recruiting friends, and it just snowballed from there."

Now four years old, Wauchope's company, Sensible Sitters, is a million-dollar business, with 300 babysitters in New York and 150 in Los Angeles.

Unlike high school sitters of yore, Wauchope's corps of part-time, in-home child-care workers are CPR-trained, available around the clock, and paid by check or PayPal. Like office temps, they sign weekly time sheets, and Wauchope sends them 1099 forms for tax filings. None are minors. Their employment contracts prohibit extreme fashions like pierced eyebrows, microminis, tattered jeans, or exposed boxer shorts while on the job. So far, she's never had to fire someone for improper attire.

"Anyone who goes to our clients' homes is representing our company, and we ask them to look as presentable as possible," says Wauchope, who wears her strawberry-blond hair in a neat ponytail. "Blue hair is not going to go on Carnegie Hill," she adds, referring to the tony neighborhood on Manhattan's Upper East Side.

In exchange for their professionalism, her sitters get a peek at the glamorous lives of well-heeled executives and celebrities and are often asked to accompany clients' families out-of-town to places like Palm Beach, Aspen, Spain, and Italy; some have even traveled by private jet to St. Barts and St. Maarten.

"It's an experience of a lifetime to be with these families," says J.J. Hennessey, 24, who has been posted by Wauchope's agency to jobs in Southampton, Sag Harbor, and Bridgehampton, three towns in New York's posh Hamptons, on Long Island.

Wauchope isn't the only babysitter-entrepreneur. Babysitting is a growing niche in professional services because, for one, its traditional source of labor has been drying up. Neighborhood teens, loaded with homework and college-application-boosting extracurricular activities, have less free time, according to Annie Davis, president of the Association of Premier Nanny Agencies, a nationwide nonprofit group. The push for professional babysitters also comes from a new generation of parents who demand more for everything having do with their precious progeny, say Davis and others.