Apple One Child iCloud Accounts vs. Regular iCloud Account?

[kat.hayes]

My two kids already have iCloud accounts that they use for FaceTime and Messaging family members. I just signed up for One and want to share Music with them. I have the option of Inviting People, or to Create a Child Account.

1. Does the Child Account create any additional protection or benefits?
2. I chose the Child Account and it wants me to enter the email address for the child so it can create a new account for them, though they already have the email addresses that I created for them registered as their iCloud accounts? What should I do?

Thanks in advance.