I think of this of the “low hanging fruit.” You can teach your child to think critically about the content they consume, and that has benefits across all media, including television, advertising (in the real world and online), and print media. It also has benefits when kids need to evaluate the folk wisdom and urban legends that parents, teachers, and friends are constantly sharing with them (see: Momo hoax). But it is not a solution (or even much of a mitigating factor) if you are concerned about the long-term effect of social media and the Internet in general.

I did touch on children’s smartphone use in a different article ( https://onezero.medium.com/the-great-smartphone-experiment-f2628bbbbdef), but as you suggest the challenges in giving young people unrestricted access to apps and content are much more difficult to address!