Sleepers

Lorenzo "Shakes" Carcaterra, Tommy Marcano, Michael Sullivan, and John Reilly are childhood friends in Hell's Kitchen, New York City in the mid-1960s. The local priest, Father Robert "Bobby" Carillo, serves as a father figure to the boys and keeps an eye on them. However, they start running small errands for a local gangster, King Benny.
In the summer of 1967, their lives take a turn when they nearly kill a man after pulling a prank on a hot dog vendor. As punishment, the boys are sentenced to the Wilkinson Home for Boys in Upstate New York. There, the boys are systematically abused and raped by guards Sean Nokes, Henry Addison, Ralph Ferguson, and Adam Styler. The horrifying abuse changes the boys and their friendship forever.
During the boys' stay at the facility, they participate in Wilkinson's annual football game between the guards and inmates, one that the latter lose on purpose to avoid reprisals from the former. Michael convinces Rizzo, a black inmate, that they should play as hard as they can to show the guards they can fight back. Rizzo agrees, and helps to win the game. As a result of this, Shakes, Tommy, Michael, and John are all beaten and thrown into solitary confinement for several weeks, and the guards beat Rizzo to death.
Shakes insists that they should publicly report the abuse, but the other boys refuse. They all therefore vow never to speak of the horrors and abuse the guards put them through once they're all out.
Fourteen years later, John and Tommy, now career criminals, encounter Nokes by chance in a Hell's Kitchen pub and kill him in front of witnesses. Michael, who has become an assistant district attorney, arranges to be assigned to the case, secretly intending to botch the prosecution. He and Shakes, who is writing for a newspaper, forge a plan to free John and Tommy and get revenge on the guards who abused them. With the help of others, including Carol, their childhood friend and now a social worker, and King Benny, they carry out their revenge using information compiled by Michael on the background and lives of the former Wilkinson overseers. They also hire Danny Snyder, a washed-up lawyer and alcoholic, to defend John and Tommy to make it seem as if their situation is hopeless.
Michael's plan will only work if he can discredit Nokes and place John and Tommy at another location. Ferguson, when called in court as a witness for Nokes' character, is forced to admit that he, Nokes, and other guards abused the boys. To clinch the case, however, they need a key witness who can give John and Tommy an alibi. Shakes has a long talk with Father Bobby, who first resists but eventually, after Shakes tells him of the abuse, agrees to lie on the stand that the accused were with him at a New York Knicks game at the time of the shooting. As a result, John and Tommy are acquitted.
The remaining guards are also punished for their crimes: Addison, an up-and-coming politician who still molests young boys, is murdered by Little Caesar, a local drug kingpin and Rizzo's older brother; Styler, now a corrupt policeman, is arrested for taking bribes and murdering a drug dealer; and Ferguson, a social worker, loses his job and family and is plagued by guilt for the rest of his life.
Michael, Shakes, John, Tommy and Carol meet at a bar to celebrate - the last time they would all be together again. Shakes remains a newspaper reporter, living in Hell's Kitchen. Michael quits the district attorney's office, moves to the English countryside, becomes a carpenter and never marries. John drinks himself to death and Tommy is murdered; both are only 29. Carol stays in the city as a social worker and has a son, whom she names after all of the four boys.

Question: What changes the boys?
Answer: The horrifying abuse; The horrifying abuse