I used to get that error when there was a brief network slowdown in my place. I think that's related to your network speed. I had my Xbox Live safety settings set up to give me no safety, but the game would still send me that annoying message :[
With a simple search, I have found another person with the same issue. http://www.minecraftforum.net/forum...7997-pe-on-ios-xbox-live-realms-login-problem
tl;dr: it's a bug. It generally happens on poor network connections. Check your network connection and restart the game.
This is actually because of the age you have set on your account, I believe if you are under 18 you cant play on multiplayer.
There seems to be a bug which displays this occasionally to normal 'adult' accounts, but restarting the game fixes that problem. This happened to me yesterday because the age I'd entered when creating the Microsoft account was under 18 - and there is no point updating that age once the XBL account has been created - it'll remain a 'child' account even if you add it to a 'parent' account and set the correct permissions in the XBOX One profile security settings (i.e 'Allow Join Multiplayer"). So if a restart of the game doesn't fix the issue, you need to create a new Microsoft account making sure you are over 18 , or you will have to be added as a 'child account' by an adult to a "parent" account, who needs to make a 50 cent bank deposit in order to prove they are an adult and then set the settings I mentioned above. Here's the definitions of 'child', 'teen' and 'adult' accounts: http://support.xbox.com/en-US/my-account/security/child-account-definition
Do you mean he didn't... enter an age less than 18? If the microsoft account age is >=18 when you create the associated xbox account then it should be an adult account, and the problem will probably fix itself when you restart MCBE. If not, it's @xboxsupport on twitter you should contact.
If you did set the age less than 18, and didn't have to go through the whole adult/child rigmarole... maybe you did it before they had put the new system in place?
Probably. Maybe it was because I set his role to "Adult" in family settings? (which strangely works despite him being 12)