FIXED - iTunes 5002 error and Unknown error in App Store and Apple family

It took a long while to work out why my child Charlotte could not log into iTunes store or App Store and received an unknown error or iTune 5002 error, which was equally helpful - NOT....

1. We used to live in the USA, I started my iTunes account in the USA.

2. We now live in Australia

3. My Child (part of my family iTunes setting thing) has an address in Australia on her account

4. Although she can be part of my family in iTunes she is unable to login to either iTunes or App Store in the US (which is my account and thus my family's account) while her address is in Australia???

I am sure there is a good reason - distribution rights or something.

It is disappointing that it took 6 hours of my Christmas evening to resolve this issue by searching on the web and talking to people in the Apple call center to work it out. BTW - no-one seemed to know this, so this is why I am putting it here.....

Simply check the address of the iTunes account (login to the manage my apple account online), compared to the app store / iTunes store that the parent/adult account has.....