How to Sign In with Apple ID on an iPad that is a child’s being managed by an adult

I manage my child’s Apple ID account and I just set her up a new iPad but I can’t figure out how to sign in with her Apple ID so she can receive her messages on the iPad and so I can make sure her iCloud backup is on because her name is grayed out in settings and there are no options for either of those if I go to her name on my phone to do it.