Over the Labor Day weekend, family and friends of Tacy Byham kept asking about her new au pair, who will arrive from Germany on Sept. 12.

"If she had been here now, she would have been hanging out with us at the pool," said Ms. Byham, 40, of Mt. Lebanon.

Such is the home life of an "au pair," a young foreigner trained in child care who becomes a member of an American host family for a year to work and study as part of a program governed by the U.S. State Department.

The name is French for "on par."

About 36,000 American families annually open their doors -- and their hearts -- to au pairs.

According to regulations, the au pair -- who is between the ages 18 to 26 -- must have at least 200 hours of child-care experience to participate.

Once situated, the au pair provides up to 45 hours of child care per week while taking six credits of classes at an accredited university.

Host families must provide an au pair with a private bedroom and access to a bathroom. Ms. Byham also provides amenities, including a cell phone, use of a car and invitations to family events, including vacations, picnics and weddings.

The benefits, said Ms. Byham, a single mother of 8-year-old Spencer Byham-Carson, include consistency of care, flexibility of hours and an intimate understanding of her child and his needs.

"I know that she will be able to pick up Spencer after school or be here when he gets home," Ms. Byham said.

A full-time leadership consultant, Ms. Byham is about to welcome her fifth au pair in the past six years. She said she and Spencer grew close to all of them and hope to attend their weddings some day.

Another benefit, said Pamela Countouris, of Cultural Care Au Pair, is that it is a "very enriching experience for families to learn about different cultures."

Ms. Countouris, of Mt. Lebanon, is the local coordinator for Cultural Care Au Pair, a provider of intercultural child care and educational exchange headquartered in Cambridge, Mass.

She serves as a liaison and a resource for 20 host families and au pairs in Mt. Lebanon, Upper St. Clair, Peters, Baldwin Borough and McDonald.

Extensive questionnaires are used to match au pairs with families, such as nonsmokers with nonsmokers and cultural lovers with those of similar bent. Phone interviews follow.

She estimated that 80 percent of the placements are successful. When they do not work out -- whether for the au pair or the family -- a replacement is found, usually within two weeks.

Ms. Countouris coordinates outings for au pairs, such as to Pirates games, and a local au pair network in which friendships often bloom, resulting in trips to malls, sightseeing jaunts and other bonding experiences.

She said the average cost of an au pair to a family is $300 per week: $175 tax-free stipend to the au pair, and the rest to cover Cultural Care costs such as airfare and training for the au pair.

"Once you get beyond a kid or two, it is the most economical program there is," said Karen Peterson, 41, of Mt. Lebanon, the married mother of three children under age 10, and whose Thai au pair is the family's third au pair in two years.

"From working parents' perspective, she is a lot of help, especially with three kids with events and school demands. Au pairs really help keep the train running on the track," said the full-time pharmaceutical sales representative.

But more important than the financial and convenience benefit, she said, is an au pair's value to the well-being of the children.

"You have someone who gets to know you and the kids and has a vested interest in being a great child-care provider because she lives with you.

She loves the children instead of it being a job," she said.

Their prior au pair plans to fly here from Germany to visit them at Christmas.

"She's definitely a part of the family," Ms. Peterson said.