How do I remove a child account from family sharing?

See the following from Leave Family Sharing - Apple Support

The family organizer can remove anyone over the age of 13* from the family group. If you need to, you can transfer a child to another family.

I have read a couple of posts where people were able to delete the account of a child under 13 years old.

How to delete your Apple ID account.         

Apple ID – How to Delete.        

Delete Apple ID (new).         

What to do after you change your Apple ID or password - Apple Support