The solution is to have filtering on the actual client devices. There need to be specialized minor-friendly devices with parental controls at the OS level, and apps need a standardized framework to integrate with those parental controls. Then create regulation that devices used by minors must have such a system, with the standard that every new action (app install, first time visiting a website, new contact, joining a group chat, etc) first needs to be whitelisted by a parent, and that parents can see a timeline of all actions.
With this solution, kids are far safer than under recent UK/EU age verification laws, while adults and their free, open & private internet remain unaffected.