There is so much instant dismissal of this entire idea that smartphones are harmful in this thread, most of which is just "correlation is not causation". Yes, correlation does not equal causation. But when it makes logical sense why there would be correlation, there is no way to actually measure causation (we can't exactly give kids placebo phones), we keep seeing the same correlation over and over again, why is it b…
The issue is that early ownership of a phone correlating to worse mental health may be a proxy for something else. If you are raising children and trying to make good parenting decisions and someone says "smartphones are the work of the devil and your child will be mentally healthier without them" they need to actually be correct, not guessing to enhance their career or something.
If it's not true, then parents who might have safety reasons for providing a phone who then opt to not provide a phone "because phones are bad for kids" may be harming their kids.
It's a blanket statement without nuance. It doesn't tell me if there are situations where it's okay and, if so, what they are. This usually means a person isn't really that knowledgeable about a topic.
People tend towards confirmation bias. It's a rare individual who says "What would affirmatively disprove my hypothesis? Does that thing exist?"
Without that, it's usually not a solid hypothesis. It's usually one full of holes.