Erm,
few scoundrels and perverts?
All the males are complicit in this— this is the basis of the religion! That’s why they’re there! That’s why they get male converts over from the outside but never any female (think about it).
This isn’t a one family and a few people. This is a lot of people organized to sexually abuse a lot of children.
OK, what would you do?
There are issues with regard to the age of consent and the minimum age at which marriage is allowed. There are issues of alleged brainwashing and coercion involved as well. The role of government, however, is not to say that so-and-so is brainwashed and must be protected, but to prosecute individuals charged with crimes. The mobility of the women and children is a problem, and a reason why it has been difficult for the authorities in Utah and the surrounding states to suppress polygamy. However, it is better to restrain the government in such matters rather than expand its authority.
Thomas More, the English jurist and Catholic martyr, warned an eager young man who would chop down all the trees in England if necessary to eliminate hiding places for outlaws that once the forests were gone, there would be no place for him to hide.