How can I remove a child from my family sharing?

For a child under 13 you can't without deleting the entire Apple ID. Do you need to remove the child at all? Just let the Apple ID stay unused for a while and any purchases made with it will remain intact for when it is next used.

If you really need it deleted: How to delete your Apple ID account - Apple Support

Read the entire link I provided. It says:

"Can I delete my child’s account?

If you are the organizer 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."