I could take you into areas of many cities where the number of underage pregnancies is triple that!

Are those pregnancies the result of adult males impregnating underage girls?
The group was still practicing polygamy, which is against the law, and teaching the children to do the same, at the very least, they could be charged with contributing to the delinquency of a minor and the men arrested for bigamy.
That bunch of people are obviously a cult but it appears most of them are there voluntarily

Cults, brainwash their members, they may THINK they're there voluntarily, but, they're not.
The Jim Jones cult members voluntarily drank poison, but only because they were brainwashed to do as he said, that's not really voluntary.