It was not that Paterno technically notified "the police." It was that, under the laws at the time, Paterno had a duty to notify his superior. He did, and there is ample evidence he did.
The only person that is charged with failure to notify (which was a summary offense at the time), is Spanier. The Commonwealth is arguing that Curley and Schultz were informed and that they, as required by the existing law at the time, reported it to their superior, Spanier. In other words, the buck stopped with Spanier under the Commonwealth's argument.
Spanier's duty was to report this to Childline, under the prosecution's theory.
The bottom line is that McQueary, Paterno, Curley and Schultz did report it according to law at the time. The law at time permitted them to report it to their respective superiors, and there is evidence they did.