Sometimes you just have to face facts--that there just isn't enough evidence to convince a jury. Based on prosecutor evidence I never believe that OJ did it, and I'll be surprised if they can do it in the TX case either. Now sometimes prosecutions are just persecutions in disguise, as a form of punishment after they fail to make the case for perceived wrongs. That is what they will probably try to do since they are treading on thin ice w/ regard to persecuting a religious sect. They will try to harass them into submission. And that is not what our system of justice is, or should be, about.
Not that I disagree with the sentiment of your comment, but the government has had little difficulty prosecuting religious sects that say, base their religion on the use of illegal drugs. In this case having a religious sect that bases their religion on polygamy is either a federal crime, like worshiping MJ by the act of smoking huge, lovingly prepared, hand rolled, joints in "mass" has been deemed to be, or it isn't.
It is going to be a problem for the State and the feds as, the law as presently written does not suggest a single or married guy who is screwing another dozen women on the "side" as it were, is doing anything illegal. But, if the dude is so dumb as to attempt to legally marry the other dozen babes he has in his corral, well, then he is doing something illegal. I see the stupid part, but don't understand the basis for formalizing the situation making it suddenly illegal. So, either polygamy is legalized, or they are going to have to make a case for their prosecution of the lifestyle. To use your terminology, it could be perceived as persecution instead of prosecution.
In any case, at the moment the arrangement is illegal, and on that basis I don't see why the kids should be left to be indoctrinated with perpetuating a lifestyle that is presently a federal crime. Even the babies and toddlers. If they were being indoctrinated to live some other form of anti-American lifestyle, I am sure you would find the situation less "grey."