From a purely legal perspective, I'd suspect that a good criminal defense attorney could successfully defend the father and the instructor against a negligent homicide charge.

From the news article it appears that the father was physically supporting the boy in handling the weapon, and was doing so under the supervision of a qualified instructor under controlled circumstances. It doesn't appear that this was some gun nut turning the boy loose with an Uzi in the back yard.

Not every tragedy is rooted in negligence, at least not negligence that rises to the high level of criminal culpability. It is possible for a reasonable person to believe that an adult, by holding and guiding an eight year old boy's arms or hands, could prevent the gun from being pointed or fired in an unsafe direction while on a supervised gun range. Indeed, it is a fairly common practice when introducing youngsters to firearms, and not incidentally, to their destructive potential.

While I do agree that criminal negligence should not be excused merely because the victim is someone the perpetrator feels particularly bad about harming, I think criminal prosecution should be reserved for the most reckless kinds of conduct. Rest assured, if you kill your child by choosing to drive while drunk, for example, you will and should be criminally prosecuted, but I don't see that kind of criminal culpability here.

Jeff