Hi George,
Thank you for posting your question here!
This is a common issue with new child accounts. The automated recovery form fails because the email has never been used so there is no email history to verify. To fix this, the password must be reset by the parent through the Microsoft Family page Sign in with the parent account go to account.microsoft.com/family select the child profile and reset the password from there. If the reset option does not appear, remove the child account from the PC only restart then add the child account again and set a new password. Additionally, do not use the security questions flow for a brand-new child account
Let me know if you need further assistance, feel free to ask me by clicking "Add Comment" or "Add Answer" if you cannot add comment so your response will be visible. Thank you and I appreciate your effort.
Regards,
Angelique P.