well, chemical castration apparently works and is used.
If the question's about physically lopping off their tackle as punishment, you might struggle to find a doctor to do it - unless there's going to be a call for public spirited volunteers?
It's not about the intercourse though, TWR, it's kicks they get from control and degradation of a child - castration's only part of the solution, IMO. Prostitutes aren't children to be frightened and made to do whatever the pervs want.