Parents should take responsibility and not let their children smoke, and we still banned selling cigarets to children. Just because something should be some way, doesn't mean as a society we shouldn't do anything about it.

In any case, the story with parents and addictive devices is even harder for parents than e.g. cigarets. For example, a LOT of schools in the UK think that it's good to give childrens ipads to study, and there's nothing that parents can do to prevent this. In this specific situation saying that "parents should take responsibility" is unfair to parents, because their only option to avoid this is home schooling.