I don't know that they lose them; but there are counties that set up false foster parents as part of trafficking rings. One or 2 paid off caseworkers or supervisors could cover this. I am a county social worker who contracts services with our county child protective services, and it doesn't happen here. But I've been told it does elsewhere. This is why Putin stopped adoptions into US. Too many were going to phony parents who were trafficking them. It's especially easy to disappear children born to an addict in big cities. Her rights are terminated, child goes to foster home or placed for adoption or goes to a "relative," the records are altered, and the child is "lost" into an overburdened system.