I would argue that they didn't do that in an official capacity because they weren't supervising the child, nor were they supervising Sandusky, nor is preventing child abuse a part of their routine job.
Further, there is no way they prevented a report from being made (ask MM), and I think arguing that the interfered with a report being made is a tough hill to climb. What did they do exactly to interfere with a report being made? They themselves didn't make a report, but they were not required to (hence the FTR being dropped), but there were numerous other people (starting with MM, but including JM, JD) who could have made a report. Even further, they reported it to JR (at TSM) which if anything is enabling a report, not preventing one.