That social worker was in an impossible situation. Its easy to say that she simply should have never brought those boys to that nut’s house. You would like to think there were some options. Sadly she probably was following strict protocols.
It sounds like the sister had made a previous 911 call regarding her brother's mental state that should have resulted in a welfare check. That would have gone in a record at the 911 center. Then if the social worker been able to give the address of the house, more data would have been available to the 911 operator.
It is great to call for a faster response to this event, but you need to know a location in order to respond.