Having been a chaperone on a number of school trips in other districts, my experience has been that all decisions and ultimate responsibility on the trip lie with the teacher in charge.
So it's hard to understand why the Orange County Sheriff's office wouldn't go directly to Mr. Behrens for information regarding parents. All other chaperones, unless they were parents of involved parties, would have no say on pursuing charges. And Mr. Behrens has made it clear that he did not tell the Sheriff's office not to pursue charges.
In addition, it seems like sloppy police work for the Sheriff's office not to speak directly with the parents, at the time of initial investigation, to ask them whether to pursue charges.