They issue is less the screen than it is the lack of long-form entertainment. Kids paying attention to an hour and a half movie plot on the screen isn't the same problem as scrolling through endless 30 second videos or accessing social media.

The TV is also bad, but smartphones are literally slot machines in the child's pocket that keep giving them dopamine hits. It's many times worse for the brain.

There are parental controls etc. But the nature of the device is addictive with its notifications and the likes.

Individually targeted and psychologically-optimized content.