Have Smartphones Destroyed a Generation?

More comfortable online than out partying, post-Millennials are safer, physically, than adolescents have ever been.

But they’re on the brink of a mental-health crisis.

One day last summer, around noon, I called Athena, a 13-year-old who lives in Houston, Texas.

She answered her phone—she’s had an iPhone since she was 11—sounding as if she’d just woken up.

We chatted about her favorite songs and TV shows, and I asked her what she likes to do with her friends.

“We go to the mall,” she said.

“Do your parents drop you off?,” I asked, recalling my own middle-school days, in the 1980s, when I’d enjoy a…