To me this highlights a weakness of Signal, which is that by being a specific organization rather than FOSS code they can be made to comply with the demands of the State

Imagine PGP or XMPP "shutting down" in UK because the State takes umbrage

Signal shouldn't have required people's phone numbers from the start. Now I don't feel sorry for them.

And besides, it's not children that must be protected from the internet. It's the internet that must be protected from children.