Granted, there is also evidence that social media has particularly harmful effects on children, which no doubt strengthens the argument. But in the general case bans targeted towards children are not (just) about that.
Ultimately the article seems to be trying to argue (implicitly) that we shouldn't ban, regulate or tax anything, because if we were to do that, we would then need to ban, regulate and tax everything in order to be "consistent". It's a common argument I see from libertarians online, including on HN. If you're going to ban guns, surely you should also ban knives and cars? If presented with a choice between permitting one specific thing or prohibiting all the things, most people will choose the former. But it's a false dichotomy. The law can treat different things and situations differently, even if those things/situations have some commonalities.