[naive]

I think historically this sort of thing is probably much less common than in past times. In the past and in most areas of poverty children were/are treated as commodities and not respected much at all. In many 3rd world countries the practices continue to this day. It's sickening and there are thousands of cases that never make the news far more sickening than the story of this fucked up girl who at least has a quasi-loving family.  There are children being sold into sex slavery literally every day. I heard a story on NPR the other day about a small boy sold to a passing man for something like 10$ USD, there was a happy ending to his story as he ended up being a national hero athlete but for most that is not the case. 



http://www.vice.com/the-vice-guide-to-t ... -episode-1
^Not porn, vice guide to travel makes documentaries about hard to reach places in the world. In this one I believe they interview some 3rd world sex workers and ask them about their childhoods. Not for the weak of heart or mind, all vice guide to travel videos are well worth watching though. Will blow your mind.