Forgot password

I set my 9yo up with a child account in 12/2020. He’s had to get a new phone due to a second round of needing screen replacement. Anyhow, I switched the SIM card into the new phone, so that’s all fine, but he can’t remember his iCloud password to get signed in and access all of his stuff. I really thought I saved this information in my notes, but apparently not. So I tried all the things I thought it would be, to no avail. So it’s now in the really horrible “recovery” process but they keep stating they’re sending him updates, etc to his apple ID (not mine, DUH) —if he doesn’t know his password how is he supposed to access that email to recover the password? I’m losing it over here! Annnnnny idea on how to get around this? I figured when I registered him as a child account, any correspondence would come to me. Apparently that is not the case. Please help!!!