Locked out of 5 Year Old Child's Account

I'm stuck in a circular loop of trying to access my 5-year-old childs account on the iPhone 7+ device they are using.

I don't remember what the password is, but to reset it, it keeps 1) saying it's sending an email to his iCloud account that uses the password that I don't know what it is or 2) sending my current phone a verification # which then sends me back to the 7+, prompting me to put in the current password which I don't know.

I am the parent and organizer on the account and I cannot change anything or unlock his account.

Help!