Fair point, but there are a couple of reasons why we would only apply this to kids. First, something can be harmful to children and not to adults. Second, even

Fair point, but there are a couple of reasons why we would only apply this to kids. First, something can be harmful to children and not to adults. Second, even if smartphones are harmful to adults, for better or for worse we let adults ruin themselves. It's a necessary condition of freedom, that you have the ability to make bad choices as well as good.