BETHESDA, Md. — ON her first morning in America, last summer, my daughter went out to explore her new neighborhood — alone, without even telling my wife or me.

Of course we were worried; we had just moved from Berlin, and she was just 8. But when she came home, we realized we had no reason to panic. Beaming with pride, she told us and her older sister how she had discovered the little park around the corner, and had made friends with a few local dog owners. She had taken possession of her new environment, and was keen to teach us things we didn’t know.

When this story comes up in conversations with American friends, we are usually met with polite disbelief. Most are horrified by the idea that their children might roam around without adult supervision. In Berlin, where we lived in the center of town, our girls would ride the Metro on their own — a no-no in Washington. Or they’d go alone to the playground, or walk a mile to a piano lesson. Here in quiet and traffic-safe suburban Washington, they don’t even find other kids on the street to play with. On Halloween, when everybody was out to trick or treat, we were surprised by how many children actually lived here whom we had never seen.

A study by the University of California, Los Angeles, has found that American kids spend 90 percent of their leisure time at home, often in front of the TV or playing video games. Even when kids are physically active, they are watched closely by adults, either in school, at home, at afternoon activities or in the car, shuttling them from place to place.