I don't know the details (and I'm not sure I want to), but I would assume they have to be doing more than a vasectomy. Otherwise, what's really the point?
I would think they would be looking to do the surgical version of chemical castration. So, I would think we are actually talking actual physical castration. Which, while I think child molesters deserve it, likely would be considered both cruel and unusual punishment under the U.S. Constitution. At a minimum, it's unusual.