Controlling what children do online is a solved problem: Parenting and parental control applications.

Spoken as someone who probably hasn't used iOS/Mac parental controls. It is a hot buggy mess that randomly blocks whitelisted applications as well. We use it, but it is a constant pain. Also a lot of applications only work half, e.g., TV apps blocking off all content rather than only content that is not age-appropriate.

By the way, we were initially firm believers of not using parental controls at all, by limiting time and teaching kids about how to use devices in a healthy way. But a lot of apps (e.g. Roblox, YouTube Shorts) are made to be as addictive as crack, making it very hard for a still not fully developed brain to deal with it.

That said, I absolutely dislike the current lobby for age verification because the goal of Meta et al. seems to be to be to absolve themselves of any responsibility by moving verification to devices and to put up regulatory walls to make it more difficult for potential competitors to enter the market. It is regulatory capture.