Hi there Rikkidees!
I'm sorry to hear that you were having trouble with the child account system. Feedback for the support articles is best left at the "Feedback" link from the bottom of Xbox.com.
This said, perhaps I could provide some guidance for users experience similar issues. Was the "8318853" error the only one you were getting? Also, is your son able to log into
https://account.xbox.com? There may be an issue with the terms of use. Are you able to try any other accounts on the console? If the child's account is new and nothing seems to be resolving
the issue, there may be a glitch on the account itself. The best step for a resolution on account specific issues would be to reach Microsoft Account support here:
go.microsoft.com/fwlink.
If the account is new, it may be easier to simply make a new account for the child. I always recommend creating the account from
http://signup.live.com (you need to be logged out for that to work), this way no information on the account is skipped. You can have the new account sign into Xbox.com from there and it should
begin the process of generating the Xbox Live profile. Note that children under the age of 13 may have difficulty participating in Xbox Live, I think this has to do with Federal Child Safety laws but I'm not 100% sure on that.