Apple ID question

From the linked article:

You can't remove a child under 13 years old from your family group, but you can move them to another group or delete their account.

You don't need to delete your own account. From the FAQ section of How to delete your Apple ID account - Apple Support:

Can I delete my child’s account?

If you are the organiser of your family, you can delete your child’s Apple ID when you request deletion of your account. Your child can also request deletion of their Apple ID, which requires your approval.

The approval request will be sent via email to the primary Apple ID email address of your family organiser account. When approving the request from this email, you'll go through the process of deleting the child account.

So presumably if you make a request from your child's device using their Apple ID you can delete their account without affecting your own. If in doubt, or for further assistance, contact Official Apple Support.

tt2