But play, it seems, isn't that simple.
Scientists disagree about what sort of play is most important, government is loath to regulate the type of toys and technology that increasingly shape the play experience, and parents still feel pressure to supervise children's play rather than let them go off on their own. (Nearly two-thirds of Americans in a December Monitor TIPP poll, for instance, said it is irresponsible to let children play without supervision; almost as many said studying is more important than play.) And there is still pressure on schools to sacrifice playtime – often categorized as frivolous – in favor of lessons that boost standardized test scores.
"Play is still terribly threatened," says Susan Linn, an instructor of psychiatry at Harvard Medical School and director of the nonprofit Campaign for a Commercial-Free Childhood. But, she adds, "what is changing is that there's a growing recognition that the erosion of play may be a problem ... we need to do something about."
One could say that the state of play, then, is at a crossroads. What happens to it – how it ends up fitting into American culture, who defines it, what it looks like – will have long-term implications for childhood, say those who study it.
Some go even further: The future of play will define society overall and even determine the future of our species.
"Play is the fundamental equation that makes us human," says Stuart Brown, the founder of the California-based National Institute for Play. "Its absence, in my opinion, is pathology."