Technology is having a major impact on how childhood is lived in 2014.

Today’s kids spend nearly eight hours a day consuming some kind of entertainment media on a smartphone, tablet or TV. At the same time, outdoor play is dropping precipitously: according to one study, kids today spend just half the time outside that their parents did a generation ago.

But now in Boston, there’s a modest attempt to change that. The Appalachian Mountain Club and Massachusetts General Hospital are joining forces to get kids and their parents outside — and using the clout of the medical establishment to make sure the message hits home.

On a weekday afternoon in Waltham, a group of parents and kids gathers to hike the Stonehurst Trails, with a guide from the Appalachian Mountain Club leads the way. With massive trees looming overhead and gravel crunching underfoot, the city feels far away. Some of these families are here because they simply wanted to get outside, but others got a gentle nudge.

Audrey Maloney is with her son Tommy, a tall, soft-spoken 10-year-old, at the suggestion of their family pediatrician. Spending an hour in the woods helps Tommy in body and mind, she said.

“He’s on the autism spectrum,” Maloney explained. “And nature and greenery supposedly is really great for calming the person, for giving them neurological growth. Tommy has a weight problem. And even though we try to not diet but curtail his diet, he needs to get physically active, and away from the addictive computers and technology.”

The Maloneys are benefiting from “Outdoors Rx,” an Applachian Mountain Club and Mass. General collaboration that trains parents to write prescriptions not for medications, but for outdoor activity.

“We have trained, I believe, over 75 pediatricians in the areas of Framingham, Waltham, and the neighboring areas,” said Dr. Christina Scirica, a pediatric pulmonologist at MGH and Outdoors Rx’s medical director. “The idea is, if you have time to plug into your screen, you have time to get outside.”

In her pediatric practice, Scirica is seeing a number of symptoms traditionally found in older patients — from diabetes to vitamin D deficiency to arthritis, Scirica said.

“These are all problems that we had historically seen in adults, and now we’re seeing more more kids,” Scirica said. “And that’s really worrisome.

The problem, she continues, is that childhood isn’t what it used to be. Many parents are overbooked and overwhelmed. They’re also reluctant to let their kids play outside the way parents a generation ago did — and the prevalence of smart phones and tablets means there’s a ready-made babysitter inside.

Problem is, the exercise that kids used to get outdoors as a matter of course is tough to replace.

“It increases bone strength. It lowers our blood pressure. It improves our insulin resistance, so it prevents diabetes,” Scirica says. “And it improves our attention and concentration— especially in kids with attention deficit hyperactivity disorder, or ADHD.”

Outdoor play also provide more subtle benefits. According to author Richard Louv, whose book, "The Last Child in the Woods", became a manifesto for a subset of concerned parents, outdoor play fosters what he calls a sense of wonder.

“Maybe you’re like me, and you crawled out through the grass at the edge of the yard where the rocks and weeds began, and you looked up into the trees,” Louv said. “And maybe you turned over a rock for the first time, and found you’re not alone in the universe.”

Louv coined the phrase “nature-deficit disorder” to describe the loss of such experiences. And he has a bold proposal: for every dollar schools spend on new technology, they should spend another dollar to get kids outside.

“What teacher wants students to be less alive? What parent? Who among us?" Louv asked.

In the meantime, programs like Outdoors Rx can have a similar effect. Participating families can choose from a host of activities, most of which are low difficulty and cost nothing. (It's worth noting, too, that a prescription isn't required to participate.)

In Waltham, after an hour hiking the trails, Tommy Maloney left the forest invigorated — by the exertion, but also by what he’d seen en route. For her part, Tommy’s mother Audrey seemed grateful that her son had received a brief taste of what her own childhood was like.

“When I was a kid, back in the '60s and '70s, literally, you were thrown out,” she recalls. “You could be 12 miles down the road, wandering the woods. You had complete freedom. Now you’re afraid to leave your kid alone in the backyard.”

“I really think [Tommy’s] interest is being perked,” she added. “I’m really hoping by the time he’s a teenager, an adult, he’ll be exploring on his own, doing the White Mountains, enjoying nature."

For the Maloneys, it seems the prescription is working.

Boston College psychology research professor and author Peter Gray discussed the benefits of unstructured, outdoor play on Greater Boston: