The success of "The Dangerous Book for Boys" — which has been on the best-seller list for the last nine months — and its step-by-step instructions for activities like folding paper airplanes is testament to the generalized longing for play’s good old days. So were the questions after Stuart Brown’s library talk; one woman asked how her children will learn trust, empathy and social skills when their most frequent playing is done online. Brown told her that while video games do have some play value, a true sense of "interpersonal nuance" can be achieved only by a child who is engaging all five senses by playing in the three-dimensional world.

This is part of a larger conversation Americans are having about play. Parents bobble between a nostalgia-infused yearning for their children to play and fear that time spent playing is time lost to more practical pursuits. Alarming headlines about U.S. students falling behind other countries in science and math, combined with the ever-more-intense competition to get kids into college, make parents rush to sign up their children for piano lessons and test-prep courses instead of just leaving them to improvise on their own; playtime versus résumé building.

Discussions about play force us to reckon with our underlying ideas about childhood, sex differences, creativity and success. Do boys play differently than girls? Are children being damaged by staring at computer screens and video games? Are they missing something when fantasy play is populated with characters from Hollywood’s imagination and not their own? Most of these issues are too vast to be addressed by a single field of study (let alone a magazine article). But the growing science of play does have much to add to the conversation.