In the end, I’ve come to the conclusion of just keeping everything as-is. I understand why using plugins/sso would be a security risk and for the children who doesn’t have email, well they can still browse the forum I guess. If they do end up wanting to join the forum, they could just ask their parents to help.
Even with verification, the forum did do much better than expected, around 30 users in the first day. I’m guessing that the verification isn’t as big of a problem then.
Thanks for all your help!