How to delete a child
How to delete a child from family sharing
iPhone 12, iOS 15
Welcome to Apple Support Community!
If you want to delete a Apple ID account, I will post a good resource below on the exact instructions for you to follow.
How to delete your Apple ID; https://support.apple.com/en-us/HT208504
Please know that When your Apple ID account is deleted, your account details and the data associated with your Apple ID are permanently deleted from Apple’s servers.
Before you Delete do the following:
> Backup data that you stored in iCloud
> download any DRM free purchases
> Make sure to sign out of any of your devices
After its deleted, you can no longer sign in to your account or access any data, content, services, or appointments that were associated with your Apple ID.
Hope this helps ;)