Thanks for your reply, sorry I have taken long to get back to you. Ok, so I went into my child's account, and have got to the point of "Change Windows Live ID". I wasn't too sure whether to proceed - if I put my email address in there as the new WLID, will that mean that it becomes the parental control one, or the child's account one? i.e. my child has their own WLID associated with the account, so I would assume that changing it would only change the child-WLID instead of the parental WLID. Man this is really difficult to explain!
To possibly make it clearer, my son's father is the current parental control WLID on our son's account. We have split up and he has moved out, so he no longer exists on our console. Would it have to be him that signs in with his gamertag, and then makes the change? I don't really want to bother him with all this, so if there is any way to do otherwise I would much appreciate it :)