So, I know of a family in the US that (years ago) agreed to host a teenager from a foreign country, but later tried to kick them out without a flight home. (Thankfully the situation worked out... not great... But it worked out).
The police never became involved, but if they had what could have happened? I can't imagine this being legal, but I can't find any similar situations. It was not the family's child, and the teen was not a U.S. citizen (but she did have a foreign family that cared about her).