@glyph @feoh FWIW I'm getting the same this eve. If I try to actually log in to the account, I get full 2FA - on her phone. And there's no details or remenants of any of these "new" devices either in the mails, via the phone, or via iCloud on the web. So I'm reasonable sure it's some bug, but I'd prefer if Apple were shouting about it, pronto.

@tinmouth @feoh Good to see more evidence for the "just a bug" hypothesis. Interesting that it's specifically affecting your kid, too; I didn't get notifications for any of my own devices, so it seems likely that it's something to do with Family Sharing.