Hello, thank you for reaching out to Microsoft Q&A.
May I please know if you no longer have access to the parent or guardian account that was used to provide consent during the creation of the child account?
If you make any security changes to your account, such as resetting your password, you'll be asked to verify your identity using the recovery email address or phone number you added during account setup.
If you no longer have access to this security information, you'll need to fill out the account recovery form for Microsoft to confirm you're the rightful owner. However, since the account is very new and has been accessed only a few times, you might not be able to provide the required details on the recovery form, making it hard for Microsoft to verify your identity. As a result, your account may be permanently lost, and there may be no other way to recover it.
While it might not be the outcome you are looking for, if you’re unsuccessful in recovering your account, then you will need to create a new Microsoft account. You can do that by clicking this link:
https://signup.live.com/
Let me know if you still need more help.