perhaps because some of the parents did not believe their children? Or because they spoke to Mr Hall and felt that that was sufficient. Or they felt it was a 'one-off incident, not realising that it had happened to other children, and that they had dealt with it sufficiently. Or they thought it was not serious enough to take to the police? Or they felt that the trauma of their child having to make a police statement woulld have made things worse? or they did report it, and no action was taken as it was not, at the time, considered serious enough to warrant further action?
Maybe the parents listened to the pleas of their children as they begged them not to tell anyone. Doing something (even the wrong thing) in the name of loving your child...is that such a bad thing?