Generally speaking you can deactivate or delete an Apple ID. Apple prefers the first because of the obvious reason mentioned below. And, I concur. See:
How to deactivate your Apple ID account https://support.apple.com/en-us/HT208503
If you request account deactivation, you'll receive a unique alphanumeric access code. When you're ready to reactivate your Apple ID, contact Apple Support, provide your access code, and we’ll help you reactivate your account. If you lose this code, we won't be able to help reactivate your account."
How to Delete your Apple ID Account https://support.apple.com/en-us/HT208504
“While your request is being processed, you can contact Apple Support with the unique alphanumeric access code you received, and we’ll help you cancel your request. After your account is deleted, Apple can't cancel the request, reopen your account, or restore your data.”
You can get additional information on both by signing in here: Data and Privacy https://privacy.apple.com/account
__________
But, are you talking about deletion in the context of family sharing? If yes, deleting your child's Apple ID may be a special case. My understanding it that this is what is involved. See Family Privacy Disclosure for Children https://www.apple.com/legal/privacy/en-ww/parent-disclosure/. Toward the end of this document you see: this heading Access, Correction and Deletion. Here is a quote from it.
"If at any time you want to access, correct or delete data associated with Family Sharing or your child's Apple ID, please contact us here: www.apple.com/privacy/contact/."
Using the above link, here is where to pursue you deletion of a child's Apple ID: Privacy Inquiries https://www.apple.com/privacy/contact/. Fill out the form provided on this link.
