One very simple way to give parents control over what their children see and participate in without violating everyone else’s privacy is to create adult and social TLDs and require these sites to migrate to them. So instagram.com becomes instagram.social, etc. Then mandate that all consumer network equipment mfrs and internet providers provide easily accessible ways to block these TLDs. Maybe combine that with some public education materials to teach less savvy parents how to do this.
Now you’ve given every parent a way to easily mass block all adult/social sites/apps if they want and no one’s privacy need be compromised.
Block how? You can block sites now and all it takes is a proxy/vpn to get around it. Nothing short of personalized age verification will work. The best we can do is make sure the age verification system is centralized by the government. The client sites can’t see who you are and the centralized government server should not be able to see the sites you visit.
The only way this can go wrong is if the client sites collude and publish their visitor logs and then the government can do the legwork to identify you. But even this is pretty easily bypassed if you use a VPN.
Reminder that the internet was created to be live and a indestructible means of reaching one and another, none of what you wrote can meaningfully do what you think it would.
Failing in parenting and lobbied politicians (regulatory capture) on the other side.