Hi, I'm John! I will help you with this.
This can sometimes happen if the original guardian who first created or managed the family group is different from the current organizer account you’re using.
If that’s the case, the original guardian will need to remove the child’s account or transfer the organizer role to you before you can make changes.
If you’re certain that you’re the only organizer, you must first “Manage Consent” for the child’s account before removing them from the family group. Once that’s done, you should be able to proceed with removing their account successfully.
Let me know if you have any further questions or concerns.