I can affirm everything that Minot and dajo said. My kids are 15 and 12 and would spend most of the day on their screens, if we let them. I bought the Haidt book, but haven't read it yet (but I saw him on Bill Maher).
Our kids are lucky: Their mom and I are both teachers and we understand the dangers. Most parents, by the time their kids are teenagers, are tired and are just glad to get a breather.
When I was a kid, I watched a lot of TV, played a lot of sports and screwed around a lot. Also hit the books enough to get into Cal. But the TV wasn't nearly as addictive as tablets and screens are now. Hell, to play with "technology" we used to get on the rotary telephone and make "phony phone calls".
At school, the kids are absolutely forbidden to use their phones in class, thank goodness. Outside of school, parents schedule their kids like crazy... at least they aren't on a screen.
It's a huge problem and I hardly even want to think about where it's headed. Even adults, they can't walk down the street anymore without ear buds, listening to a podcast or something. Then, surprise, they get mugged or hit by a car.