My guess would be that this was a firearms safety demonstration. The gun almost certainly had to have been handled in some manner. I mean why handle it, in that situation, it if not using it to demonstrate firearm' safety to the children but if so - why use a live weapon with live ammo at all. If that guess is correct, then I offer my opinion, based upon years of firearms handling and 14 years of collateral duties as a firearms instructor, that the officer was negligent, as were his commanders, in allowing a live firearm and live ammunition into the same room in which such a demonstration was being held before young students. The gun that should have been used for such a demonstration: a non-firing model, either manufactured for demonstrative purposes only or an actual firearm that had been modified as incapable of firing such as one in which the firing pin was grounded down or removed. In addition, there was no need for live ammunition to be in that room during the demonstration, certainly not in the same caliber for the gun being used as a prop.
As of right now, it has been reported that "details are sketchy". If though, this went down as I suspect, with the officer negligently possessing a loaded working firearm, then negligently exhibiting and then negligently firing said weapon and wounding three children as a result, all I can say is I think that he turned it into a Red Ribbons of Blood Week for those kids. How ironic would it be now, in light of the fact that this was an anti-drug program, if some of these students turned to drugs to help them cope with the psychological trauma some of them (or their parents and lawyers) are almost sure to report they have suffered because of this incident.
All the best,