People like to make fun of and poke holes in the EU's planned implementation of this, but so far they seem to be the only ones trying to implement this in a way that doesn't give my name to every online service or give some identity provider full knowledge which services I sign up to

The California bill about setting an age in the OS was another interesting idea. Have the parents police a single setting on the device, then websites and apps can query that setting. Of course that's little more than the parental controls we always had, but apparently everyone forgot about those