When I was a kid, childhood meant playing on the street, riding my bike, hanging out with friends.
Most kids now experience a different childhood.
Jonathan Haidt's bestselling book, "The Anxious Generation," talks about that. He calls it "a tragedy in two acts."
"Act One, we lose the play-based childhood. We stop letting kids run around outside. We're too afraid they'll get abducted. ... We get gradual loss of play from the '90s through the early 2010s. ... That sets kids up to be weaker."
Because kids who don't have real experiences are less resilient.
"If you have a play-based childhood with no adult supervision," says Haidt, "you learn to be self-supervising. Sometimes you get lost and you're scared, but you find your way back. Sometimes some mean kids threaten to beat you up, but you either talk your way out of it or run away. ... Those sorts of things toughen you."
Today's kids face a different reality.
"If all you do is sit inside on a computer, you're missing out on your childhood. That brings us to the Second Act of the tragedy, which I call the 'great rewiring of childhood.' Between 2010 and 2015, everything changes ... you get higher video speeds, on-demand porn. You get everything in this little box ... If you spend five to 10 hours on your device, there's a lot of things you're not doing ... Sleep goes down, time with friends goes down, exercise goes down."
In 2010, he says, people ages 18-24 spent a couple hours a day hanging out with friends. Not today.
"Once they get a smartphone ... time with friends plunges. But one of the best things you can do as a kid is hang out with friends, joke around, have adventures."
Haidt proposes four things to help reduce the damage.
No. 1: No smartphones before high school.
No. 2: No social media before 16.
No. 3: Phone-free schools.
No. 4: Far more unsupervised play and childhood independence.
This is needed, he says, because "Kids have been shifted from 'discover' mode into 'defend' mode. They are anxious; they're not risk-taking. Kids need far more independence, free play and responsibility in the real world."
He's convinced many parents and governments.
"All around the Western world, people are acting on the first three: Parents are fed up with phones, teachers are fed up with not being able to reach kids."
Recommendation No. 4 is tougher, he says.
"Convincing parents that they need to back off, send their kid out to play, not monitor them every moment, is a much harder sell."
To promote his recommendations, he's partnered with "Free-Range Kids" author Lenore Skenazy.
"She and I co-founded an organization called Let Grow. We're advocating for giving kids back independence that will lead to them becoming competent, capable, happy young adults. We propose that schools and families work together to give kids a lot more unsupervised time."
"Let them play freely and maybe get hurt?" I ask.
"The world is much safer now than it was when you and I grew up. Drunk driving is way down. Crime is way down. Kids are much less likely to be harmed."
But parents and kids don't realize that. It's a reason college students, he says, fear the world.
"Our stereotypes about college students were that they're in 'discover mode,' up for fun, eager to go to parties. It's only in discover mode that you learn anything. ... (But today) they're much more in 'defend' mode."
In our full hour-long interview, Haidt and I talk about how his work has already persuaded lots of schools to ban cellphones during the school day.
In addition, more than 1,000 schools are trying the (free) Let Grow Experience. One monthly homework assignment: Go home and do something NEW on your own.
Having a life is what makes kids sensible and strong.
Every Tuesday at JohnStossel.com, Stossel posts a new video about the battle between government and freedom. He is the author of "Give Me a Break: How I Exposed Hucksters, Cheats, and Scam Artists and Became the Scourge of the Liberal Media."