How can I remove a child account that is under 13?
How can I remove a child account that is under 13 from family sharing?
Question marked as
You cannot remove a child under 13 from Family Sharing. You can transfer the child to another group but you cannot remove them in your own. As stated in the references support article in the upper left corner of this web page.
Remove someone from your family group
The family organizer can remove anyone age 13 or older* from the family group. If you need to, you can transfer a child to another family.
If you really need to remove this child and can’t move them to another family group, my suggestion would be to contact Apple directly and see if they can help.