And we're not just talking high school students; this practice of hovering often begins before they've learned how to write. Kids used to grow up in a neighborhood-- on the block or in the parks, playing games with other kids. These games had rules, but the kids themselves determined them, flexing their imaginations. Social scientists called these activities -- capture the flag, bike races, pickup baseball games -- "free play, " and it's been steadily decreasing since the 1950s. Scientists have also noted a correlation between the decreasing amount of childhood free play—any play not directed by adults—and the increasing rates of anxiety and depression among kids. As free play decreases, anxiety increases.

Kate Fagan