Can I create an icloud email address for my child when they already have an existing Apple ID with their gmail account?

Can I create an icloud email address for my child when they already have an existing Apple ID with their gmail account? I set my child up with their own Apple ID with the gmail account that I created a long time ago, can I create a new icloud email address to associate with their current Apple ID? Do I do it through the family setting to create the child account? Thanks!