Serious question, if you have kids how do you keep them safe online? I'm thinking just keep them offline. Literally. If they want to know something, download it for them, give them that data in some form for them to consume offline. If they want the freedom to search, compile a compendium YOURSELF of things you feel are appropriate for them at the time. They then have a massive offline encyclopedia to enjoy free from any potential traumatic interactions.
1) is unfeasible
2) destroys social life (important)
3) harshly limits their ability to learn independently
4) is the digital equivalent of locking them in the basement