I think that the isolation in which these people have lived, mistrusting the outside world, is the problem. If the LDS church would allow polygamy, now that it is not illegal, then FLDS could merge with them.
As for the children, culture shock would further traumatize them. Foster care with emotionally healthy LDS families (if there are any such

) may be the best option to transition these children to the outside world.
LDS bears the responsibility. If they are willing to take it.
If this is all they have known, and they do not know it is abnormal or illegal, and have been taught (or terrorized) to deny thier feelings-- and believe that they had no rights--