It might seem obvious. Parents know when their children are playing, whether it's a toddler scribbling on a piece of paper, an infant shaking a rattle, or a pair of 10-year-olds dressing up and pretending to be superheroes.
But even Merriam-Webster's Collegiate Dictionary definition, "recreational activity; especially the spontaneous action of children," is often inaccurate, according to scientists and child development re-searchers. Play for children is neither simply recreational nor necessarily spontaneous, they say.
"Play is when children are using something they've learned, to try it out and see how it works, to use it in new ways – it's problem solving and enjoying the satisfaction of problems solv[ed]," says Diane Levin, a professor of education at Wheelock College in Boston. But Ms. Levin says that, in her class on the meaning and development of play, she never introduces one set definition.
"This is something that people argue about," she says.
Scientists and child advocates agree that there are many forms of play. There is "attunement play," the sort of interaction where a mother and infant might gaze at each other and babble back and forth. There is "object play," where a person might manipulate a toy such as a set of marbles; "rough and tumble play"; and "imaginative play." "Free play" is often described as kids playing on their own, without any adult supervision; "guided play" is when a child or other player takes the lead, but a mentor is around to, say, help facilitate the LEGO castle construction.
But often, says Dr. Brown at the National Institute for Play, a lot is happening all at once. He cites the time he tried to do a brain scan of his then-4-year-old grandson at play with his stuffed tiger.