I don't necessarily think it's an ethically bad idea, but "banning all children from all social media" is simply impractical for many reasons, including:

- You essentially have to check some sort of ID and ban VPNs, banning online privacy which is BAD

- The smartest kids are way more tech-savvy than the dumbest adults, so you may end up banning adults too, which is BAD

- What will you do to children who get caught? Jail them? Call their parents, teachers, etc. who may not care? Make them take a "social media rehabilitation" classes? Consider that no matter the penalty, many, many kids will try very hard to work around this, and many parents will actively support them.

Something which would actually work is "banning" children like we ban them from seeing Rated R games and movies. Like:

- Banning children from specific social media sites (e.g. Facebook, Twitter, Instagram). This can be done through laws or just activism and lobbying to pressure the sites into banning children themselves

- Encouraging parents to ban children from social media, teaching them how. You cannot call CPS on parents whose children are using social media, unless you think having many, many kids in foster care is a worthy sacrifice

- Creating stronger parental controls (which is also a part of 1 and 2: individual sites can create stronger controls like ID to ban children, and stronger parental controls will help parents)

- Simply discouraging children from using social media, maybe even with incentives