Jonathan Haidt is a social psychologist who believes that your child’s smartphone is a threat to mental well-being. His new book, The Anxious Generation: How the Great Rewiring of Childhood Is Causing an Epidemic of Mental Illness, hit the No. 1 spot on the New York Times’ best-seller list.

This book has struck a chord with parents who have watched their kids sit slack-jawed and stock still for hours, lost in a welter of TikTok, Instagram, Snapchat, Twitch, Facebook, and more. Haidt blames the spike in teen-age depression and anxiety on the rise of smartphones and social media, and he offers a set of prescriptions: no smartphones before high school, no social media before age sixteen.

His concern is with a lack of protection for the young in the virtual world. Tech companies and social-media platforms have been “designing a firehose of addictive content.” This is causing kids to forgo the social for the solitary and have “rewired childhood and changed human development on an almost unimaginable scale.” He continues:

In 2008 the original iPhone was an amazing Swiss Army knife. It was one of the greatest inventions of humankind. So, if I wanted to get from point A to point B, hey, there’s a mapping function. If I want to listen to music, hey, there’s an iPod, and it was not harmful to anyone’s mental health.

But then a couple things changed in rapid succession, and the smartphone changed from being our servant to being our master, for many people. In 2008, the App Store comes out. In 2009, push notifications come out. So now you have this thing in your pocket in which thousands or millions of companies are trying to get your attention and trying to keep you on their app. In 2010, the front-facing camera comes out; in 2010, Instagram comes out, which was the first social-media app designed to be exclusively used on the smartphone.

So, the environment that we were in suddenly changes. Now the smartphone isn’t just a tool; it is actually a tool of mass distraction. What I mean by “the great rewiring” is this … once we get super-viral social media in 2010, a lot of things change. Now it’s not just “Hey, I’m bored, let me play a video game.” It’s “My phone is pinging me saying, ‘Someone cited you in a photo. Someone said something about you. Somebody liked your post.’” We’ve given these companies a portal to our children. They can control and manipulate them, send them notifications whenever they want.

I’ve heard stories from Gen Z. They go over to their friends’ houses sometimes—not that much—and they’re on their phones separately. One might be watching her shows on Netflix. One might be checking her social. ... There’s a wonderful phrase from the sociologist Sherry Turkle: “Because of our phones, we are forever elsewhere. We’re never fully present.”