Child under 13, forgot password. was not able to reset and now says username doesn't exist

My 8 yr old forgot his password. I tried to reset it, but was unable to do so. Now, the user name is still listed in my family share, but we have no way to recover it, or delete it (since he's under 13). I have 5 children, and no more space in my family share to just leave that account and create a new one. I did email when attempting to reset password, and got nothing. But since then, it states his username doesn't exist? Im not sure if I'm explaining it correctly or clearly. I use a 2020 SE, and we have tried on his iphone 6 and a siblings iphone 7. I just need to either delete his profile and create a new one, or reset his old user info with a password *I* will remember.