Hiring a part-time nanny seemed like a simple thing to Peggy Seiter. The job she planned to offer — $250 for four afternoons of work a week, plus school holidays — seemed attractive.

But making a deal proved harder than she expected. After interviewing a string of unsuitable candidates, Ms. Seiter, an actuary and mother of two in Rye, N.Y., had to raise her offer to $400 and add a full additional day of housecleaning work to lure the nanny she wanted. “You don’t really reduce your costs very much” by hiring a part-time nanny, she says.

While no national data exist, placement agencies and Web sites are seeing a surge in demand for part-time babysitters, posing new challenges for families. At Childcare Solutions, a Beachwood, Ohio, agency, part-time placements have risen to 62% of all hires from 57% in 2003, says Michael Gerard, executive director. Sue Kauder of Quality Care Associates, Rye, N.Y., says 15% to 20% of her placements are part-time, up from 5% in 2003. In Philadelphia, Wendy Sachs of the Philadelphia Nanny Network says 30% of parents who call want part-time rather than full-time help, up from 17% in 2004. Online postings for part-time child care on such Web sites as www.CraigsList.org are rising, too.

While the total wages paid a part-time nanny are still lower, the demand has pushed hourly rates to full-time levels and above, narrowing the savings parents can expect. Part-time nannies are earning from $13 an hour to as much as $20 to $25 in affluent areas such as Silicon Valley and Westchester County, N.Y., based on interviews with several nanny agencies. That compares with roughly $10 to $18 for full-time nannies. Many parents also are finding they must expand job duties or offer flexible hours or paid vacation to attract the candidates they want.

Changes in family life are fueling the trend. Mothers and fathers are patching together a combination of child-care setups to reduce the need for paid help. Some are telecommuting part-time to oversee the kids. The number of employees who bring work home nights and weekends has risen to 20 million from 18 million in 2003; 51.2% of them have children under 18 at home, well above the 39% average for all U.S. households, says IDC, a Framingham, Mass., market-research concern.

A growing emphasis on the importance of preschool education is leading more parents to split child care between preschool and a nanny. Preschool attendance among three-year-olds rose to 42% in 2002, the latest data available, from 38% in 1998, says Rand Corp., a research concern; 67% of four-year-olds are enrolled. “In the past, people needed full-time nannies for three-year-olds. Now, even two-year-olds are doing half-day preschool,” says Suzanne Royer-McCone of Annie’s Nannies Inc. Household Staffing, Seattle.

Many at-home parents are also hiring part-time help to manage a growing array of volunteer and extracurricular activities. Ronda Breier, Los Altos Hills, Calif., employs a babysitter about 14 hours a week to care for her four-year-old son while she volunteers at her two older sons’ schools.

The trend poses recruiting challenges for parents. Most trained, experienced nannies want full-time work. Graduates of the English Nanny & Governess School, Chagrin Falls, Ohio, which accepts just 30% of its applicants and trains them rigorously, seldom work part-time, says executive director Bradford Gaylord; “they’re able to choose full-time positions, so they do.”

Agencies can be good matchmakers, but they cost. Ms. Seiter found her part-time babysitter through Quality Care. Agency fees generally range from $450 to $2,400, varying by region and services offered. They may run 10% to 13% of the employee’s annual gross pay, or, for temporary part-timers, a daily fee of about $15 to $20. In return, agencies recruit and screen applicants and usually guarantee a free replacement if a new hire quits within two to six months.

Parents also often post ads online. This can work especially well in university towns, where students may be seeking part-time work. However, Web sites don’t always attract top-tier applicants. Annie’s Nannies rejected one applicant whose parent reference said she shouldn’t work with children — she was neglectful and secretly entertained friends while working. Although Ms. Royer-McCone didn’t suggest the applicant turn to the Web, she later saw her “Position Wanted” ad posted on CraigsList.org.

Parents who recruit online need to set aside plenty of time and energy for screening applicants, including a background and driving-record check — though this can be difficult for busy parents. Shari Boxer Baker has spent dozens of hours in the past few weeks doing phone interviews with people who responded to her CraigsList.org ad for a part-time babysitter; screening “has been my own part-time job,” says the Los Gatos, Calif., public-relations-agency owner. She received nearly 70 responses and has trimmed candidates to six. Before hiring, she’ll insist on three child-care references and check each carefully.

Some parents try sharing child care. For a while, Ms. Breier and other mothers in her son’s play group cobbled together a shared 35-hour-a-week work schedule for Ms. Brier’s nanny. Over time, however, “all the other families faded away,” changing child-care setups, she says. Fortunately, Ms. Brier’s babysitter found a part-time coffee-shop job with benefits to fill out her schedule.