There is sadly not even a mention of correlation in the title, and the post heavily implies (except for a single paragraph, which is very late in the article) this correlation implies causation. Which it doesn't, and that's imporant! For all we know, households that yield kids with worse mental health also happen to give them smartphones younger. Perhaps the parents are more disinterested, perhaps the parents have worse impulse control. Perhaps one of those things are the issue.

This is insufficiently discussed, which invites the reader to dismiss the premise. This is bad, because it might also be true. In essence, highlighting it's own criticism a bit more strongly would have gotten the point across better.