Imagine a drug that could enhance a child’s creativity, critical thinking and resilience. Imagine that this drug were simple to make, safe to take, and free.

The nation’s leading pediatricians say this miracle compound exists. In a clinical report, they are urging doctors to prescribe it liberally to the children in their care.

What is this wonder drug? Play.

“This may seem old-fashioned, but there are skills to be learned when kids aren’t told what to do,” said Dr. Michael Yogman, a Harvard Medical School pediatrician. Whether it’s rough-and-tumble physical play, outdoor play or social or pretend play, kids derive important lessons from the chance to make things up as they go, he said.

The advice, issued by the American Academy of Pediatrics, may come as a shock to some parents. After spending years fretting over which toys to buy, which apps to download and which skill-building programs to send their kids to after school, letting them simply play — or better yet, playing with them — could seem like a step backward.

Pediatricians insist that it’s not. The academy’s guidance does not include specific recommendations for the dosing of play. Instead, it asks doctors to advise parents before their babies turn 2 that play is essential to healthy development. It also advocates for the restoration of play in schools.

“Play is not frivolous,” the academy’s report said. It nurtures children’s ingenuity, cooperation and problem-solving skills — all of which are critical for a 21st-century workforce. It lays the neural groundwork that helps us “pursue goals and ignore distractions.”

When parents engage in play with their children, it deepens relationships and builds a bulwark against the toxic effects of all kinds of stress, including poverty, the academy said. In the pediatricians’ view, essentially every life skill that’s valued in adults can be built up with play.

“Collaboration, negotiation, conflict resolution, self-advocacy, decisionmaking, a sense of agency, creativity, leadership, and increased physical activity are just some of the skills and benefits children gain through play,” they wrote.

The appeal comes as kids are being squeezed by escalating academic demands, the encroachment of digital media — and its rising risks of obesity and sleep deprivation, and parents who either load up their schedules with organized activities or who are themselves too busy or stressed to play.

The trends have been a long time coming. Between 1981 and 1997, detailed time-use studies showed that the time children spent at play declined by 25 percent. Since the adoption of education reforms in 2001, public schools have steadily increased the amount of time devoted to preparing for standardized tests, cutting deeply into recess and free play.

By 2009, a study of Los Angeles kindergarten classrooms found that 5-year-olds were so burdened with academic requirements that they were down to an average of 19 minutes per day of “choice time,” when they were permitted to play freely. One in 4 Los Angeles teachers reported there was no time at all for “free play.”

Increased academic pressures have left 30 percent of U.S. kindergarten classes without any recess.

Pediatricians aren’t the only ones who have noticed. A consortium of educators, health professionals and child advocates called the loss of play in early childhood “a tragedy, both for the children themselves and for our nation and world.” Kids in play-based kindergartens “end up equally good or better at reading and other intellectual skills, and they are more likely to become well-adjusted healthy people,” the Alliance for Childhood said in 2009.

The decline of play is a special hazard for the roughly 1 in 5 U.S. children who live in poverty. These 14 million children most urgently need to develop the resilience that is nurtured with play. Instead, Yogman said, they are disproportionately affected by some of the trends that are making play scarce: academic pressures to improve test scores, outside play areas that are limited or unsafe, and parents who lack the time or energy to share in playtime.

Yogman also worries about the pressures that squeeze playtime for more affluent kids. “The notion that as parents we need to schedule every minute of their time is not doing them a great service,” he said. Even well-meaning parents may be “robbing them of the opportunity to have that joy of discovery and curiosity — the opportunity to find things out on their own.”

UCLA pediatrician Carlos Lerner acknowledged that the pediatricians’ new prescription may meet with skepticism from parents, who are trying to give their kids a leg up in the world.

They should welcome the simplicity of the message, Lerner said. “It’s liberating to be able to offer them this advice: that you spending time with your child and letting him play is one of the most valuable things you can do,” he said. “It doesn’t have to involve spending a lot of money or time, or joining a parenting group. It’s something we can offer that’s achievable. ”