I think when a child or adult is forced to have sex, it is rape. I think that when a child or adult is basically sold to another person, forced to be legally bound to that person, forced to have sex with that person, it is sexual slavery. If it were just a question of age of consent, I could go with cultural relativist arguments more easily. I'm glad the state of Texas took all those kids away from that polygamist cult that was marrying young girls off to adult men.
Hundreds of Yemeni women did show up outside Yemen's parliament to support a law stating the minimum age for girls to marry to be set at 17 (for girls) and 18 (for boys).
linky
The statistics regardng sexual abuse/assault of children in the US vary, but it's in no way uncommon. People just don't have to marry their victims here to gain access to them.