While I agree how unfiltered content can be damaging to children's minds and social media platforms should be held liable for continuously feeding children with unfiltered content, does not mean that all the blame goes to the social media platforms. Internet in general can be dangerous with children and as long as parents leave their children unattended while surfing the internet, they could be exposed to far more dangerous stuff in the internet. What I'm saying is that, parents should act as parents to their children, set parental controls on their devices to restrict their internet usage and the sites they can see then when they get exposed on harmful things in the internet, parents should be there to properly guide and explain things to their children.
In terms of banning social media platforms for children, I do not have a problem with it but I do not know how the platforms can implement it. Maybe by adding KYC for each users to make sure they are above the age restriction but that can lead to security and privacy issues.
I agree, it's the parent's responsibility to say, no you little fucker, you're not having social media.