At lunchtime on a typical weekday, birds outnumber people in Western Springs, Illinois. This old suburb, marked by tidy brick homes, is so startlingly green that you can imagine the former prairie straining beneath the surface of the sidewalks and lawns. The town may be less than 20 miles from Chicago’s Sears Tower in one direction and from O’Hare International Airport in another, but with children at school and parents at work, peace and stillness reign over all.

Then Aileen Pendleton comes home.

Out of her silver minivan pour the children: six-year-old Anna, fresh from her half day at kindergarten; five-year-old Hunter, eager to plant tomato seeds in the backyard; shy three-year-old Malcolm ("Mac"), who, as always, trails after Hunter; Elizabeth ("Ellie"), two years old, an elfin-faced toddler; and the baby, Emma, 10 months, who observes it all from Aileen's arms.

Within seconds, Aileen's small house and yard are roiling with kids — squabbling, planting, laughing, playing, and guzzling formula. It may not be peaceful, but that's OK. The noise and tumult of five adored children are the sound track Aileen, 33, has chosen for this period of her life, and that choice has enriched not only her own family but the one across the street. Across the street, you see, lives Alison Weber — Aileen's older sister, her closest friend, and the mother of three of the five children in Aileen's daily care.

The sisters' arrangement, in which Alison works outside the home while Aileen cares for the kids, is a fusion of convenience, symbiosis, and good, old-fashioned Kismet. Financial contributions by Alison have helped make it doable for Aileen to stay home with her two children, Ellie and Hunter. For 37-year-old Alison, having her three kids well cared for within the embrace of family is especially reassuring as she commutes to Chicago each day. She can commit herself fully to the job she loves, as senior vice president for marketing at Levy Restaurants, a Chicago-based company that provides food at sports and entertainment venues and owns restaurants around the country. "I don't think I would still be working if I didn't know my kids were loved all day," says Alison. "All our lives are better because of what we have."

When Alison and both husbands return in the evening from their jobs in Chicago (Neil Pendleton is a project manager for a real estate firm; Peter Weber also works at Levy), the kids divide by surname: Anna, Mac, and Emma Weber go home with Alison; Ellie and Hunter Pendleton stay put. Then adult time begins: Aileen and Alison usually conclude their day with a walk through the neighborhood, and Peter and Neil occasionally share a beer. "Our parents were Scottish immigrants and first-generation Americans," says Alison, who, like her sister, has dark brown hair, freckles, and a warm, welcoming smile. "They instilled in us that family is the most important thing you have. Because we live across the street, our kids see that you can have that family feeling beyond your immediate siblings."