I have friends with kids on all side of this coin:

Group A is tech parents with screen time control ( uses parental controls)

Group B non tech parents with physical screen time ( takes phones away)

Group C parents that let the child decide ( kids have full control over own devices)

And without a doubt one can notice developmental diviations in the children av group c. They are not very active, hard to socialize etc.

Group bs children are usually way more phydicsl about things.

But bottom line is that tech is negatively impacting children if left unsupervised.

And i honestly think much of that comes down to design patterns in apps. We make stupid apps be addictive to adults to optimize engagement and these same physiological hooks work on children except way more potent.