As an elder millennial I can remember everyone being absolutely glued to MSN Messenger in secondary school. This was back in the dialup days so it was stopping your parents making phone calls!
Regardless, I feel that it the debate needs to be about what children are doing. Probably like many here I spent a lot of my childhood devouring technical content on the internet, which I would say has given me the chance to work on incredibly interesting projects (and make friends with people across the world). If I had been time restricted on my computer (and a lot of my friends were) it would have significantly altered my career trajectory.
If you are scrolling endless garbage tiktok or YouTube videos for hours a day, yes the utility is pretty low (though again, watching hours of trashy cable TV back in the day doesn't feel that different to me).
That doesn't mean that many won't learn and find out about their passions in a way that was unthinkable a few decades ago.