Why not use the emails you guys already have? I don’t think I or even you guys would want to use an email created by parents, since the username might not even be something they would have chosen for themselves.

Let them have an email when they are old enough to create their own. Use something like simplelogin maybe instead for an alias email instead that still comes to your email but looks separate for relatives it is sent to? I wouldn’t want a premaid email account of my own before I was old enough.