Login problem with child account on xbox
I have created a child account for my child in FC24 on Xbox but when we try to log in with their username and password the game just returns to the login page without logging them in. There are no error messages, it just goes back to the login page. I have checked the username and password are correct. There is nothing about this on the help pages. We have tried restarting the game and restarting the Xbox but the same thing happens every time.
Additionally I can't see my child account in manage my account on the EA website. The help pages say I should use the "EA app" to manage a child account but there's no EA app in the Google play store or for the Xbox. The child account must be linked to my email address because I created it following the link in the "create an EA account for your child" email. Why doesn't it show under my account?