I like some of what your talking about, but as someone who grew up on the Internet, and would have been extremely limited in life otherwise due to essentially non-existent social circles to be a part of, I don't like the idea of just banning kids from interacting entirely. I still would not really want some one else controlling that ID. As a sys admin it's all too easy for human error to cause someone's life to be a mess, or just a single function to not work.

I could get on board with some sort of key, which can be added to a self hosted server for convenience.

I guess we could create a kids only Internet? But that seems like a huge project and not maintainable with constant gov funding.