Informed, in 1976, by the child himself. From the NY Times story:
The accuser said that he cried out when Mr. Sandusky penetrated him with a finger, a cry loud enough for other campers to hear, and that he later reported Mr. Sandusky’s inappropriate behavior to adults at the camp. The next day, the accuser said, he sought out Mr. Paterno and described the encounter in the hallway of a football office building as Mr. Paterno was on his way to a meeting.
“Is it accurate that Coach Paterno quickly said to you, I don’t want to hear about any of that kind of stuff, I have a football season to worry about?” a lawyer for the insurer asked the accuser, according to the deposition.
“Specifically, yes,” the man replied.
Another victim, after reporting being assault by Sandusky to a staff member of Nittany House, a male-only home for troubled youth, was threatened with juvenile prison unless he wrote an apology letter to Sandusky
While Sandusky and the other man left, Doe was informed by Gordon he would have to pen an apology letter to the pair for “telling lies,” and that his time at the Nittany House was likely coming to an end. As a homeless youth, Doe knew the unnamed alternative option.
A: ...the threat all along was that if you had to get removed from Nittany House, you got put into Centre County Youth Detention until they figured out what to do with you after that, send me to another group home.
Q: Which is a more serious—
A: It’s a prison for juveniles.
He avoided writing the apology by, basically, running away from the home:
Declaring himself done with the ordeal, Doe walked to a closet in the house, grabbed a coat and “just hauled ass,” sprinting out and away from the house at 9 a.m. He was eventually caught and placed in another facility, absolving him of Gordon’s apology letter requirement.
Q: So at no point did you write the apology letter?
Q: —that Mr. Gordon described?
A: No. But the minute I walked out of that door, their responsibility was to notify the police, and as far as they were concerned, I’m sure I was not their problem anymore.
Sandusky's M.O. was to victimize the most vulnerable young men in his community. And he was protected, over and over again, by those who were charged with ensuring their welfare.