In countries where it was illegal... human trafficking... so definitely minors involved at some point. It's something sickening enough to drop a person who I've developed feelings for. There was a sex trade survivor who was repeatedly raped by their father, given off to men of all statuses. Read about her experience here and cringe to sleep on continuing to desire a man that was potentially involved in something like that:
https://www.reddit.com/r/AMA/comments/8o7ueo/i_was_forced_into_the_sex_trade_by_my_father_sold/