A parish to which I once belonged had a pastor who sent to certain classrooms for girls to " help count money  ".  
I will not recount here what he did to them  .
The Sisters who ran the school packed up and left in protest  .  He bad- mouthed them from the Sunday pulpit  .  
The lay women tried sending him younger girls .  He complained  .  He had one age level no girl younger or older  .
Absolutely  :  access !!!    is the key . Boys are targeted for this reason  .  
Maybe teen boys represent the adult's  same-sex attractions .    I don't know  . 
The local police it seems had so many files over decades they threatened the diocese to give to the press  .  This pastor continued to visit parish grounds and his friends threw a big to-do for him to celebrate 50 yrs. being ordained .   Party took place place in large church hall  .  
It took many years to face and admit the harm done  .