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.