Adult leaders in boy scouts are what is called mandatory reporters. This means that when they have a real suspicion or evidence of an instance of child abuse, or fighting or bullying or harm to a child, they have to report it to the relevant authorities. If it is an event at a scout event the relevant authority is the scout executive – otherwise it is your local child protection agency.
This is one of the responses that the BSA has taken to head off a scandal because of weak responses in the 1970′s and 1980′s. Unlike Penn State or the Catholic church, they took the problem seriously and are now in the lead with a good reputation.
I recently had to go through this process (I cannot say anything about why or where). What happens is that you eventually get through to a skilled professional scouter. He (at AAC) listens to what you are aware of and if he thinks it may be reportable gets a written description. The written description is then reviewed by BSA’s legal counsel at National Headquarters and then the executive is told whether to report it or not. Simple, easy and straightforward.
The difficult part of this is not the professionals. You will upset some people in your unit. I’ve had threats, insults and demands to resign. All for following as closely as time allowed the guide to safe scouting. No one ever said doing the right thing was easy – but it is part of what we teach the scouts and what we swear to do as eagles.