So many questions!!!! First, the country/ state this is happening in makes a difference re. laws that are to be followed. The amount of access one has to communicating with the child, his/her school teachers, his/her other relatives will make a difference. Is everyone in the child`s life aware of the danger to the child and keeping an eye out for tell tale signs? Does the child have access to help or people to confide in if there are problems? Age of the child may be relevent too?
Sometimes the system that is supposed to look after societies children (who have no one to look after them) is so pitifully under funded they turn a blind eye to problems such as the one you have mentioned.
I hope someone here can help with specifics. I wonder if any of these agencies who are turning a blind eye could be threatened with being sued if the situation does prove dangerous for this child....ie negligence??? You may as well try any trick you can to put this case on top of the pile. Good luck, let us know! What you are doing is important and you are going to make a difference in someones life.