A few days ago, I signed up for the family premium plan and invited my daughter to connect. To accept the invite, you have to login to the web interface but when I checked her account name, it's all alpha numeric characters. I remember reading this could be problematic with Facebook but she doesn't have a FB account.
I don't want to setup a new profile for her for fear of losing the history on her current profile. Not sure how to resolve this.
When you create a new account, you'll be able to choose any username, even if it's already taken. You'll log in with your email address as a username however.
These accounts get a randomized username assigned to them which the user isn't supposed to see. The same applies for Facebook-created accounts. Instead of the alpha-numeric username, users see their Facebook name. It does happen in some situations that this username may be visible somewhere in the UI. Could you let us know where you see this username? A screenshot would help a lot.