This would be trivial to implement well. Give the parents a console where they can paste in usernames. Most classes already have parents whatsapp groups or similar, so it’s easy enough to broadcast the usernames, or create a shared google doc.

Console access could also be required to create new accounts. The article says it is currently trivial for kids to just create an adult account and bypass all the parental controls.

I don't think it's a terrible idea. You could make the keys some sort of amiibo-like NFC device or trading card.

There is probably some way you could toy-ify it and sell a lot of units

Parents have whatsapp groups for their kid's classes? That's news to me. When did that become the norm?