How do you go about teaching firearm safety to a 4-Year old kid? And I doubt he know's Cooper's four rules. The sad thing here might be that we're still cracking jokes and talking about our rights while a 6-year old kid suffers.
This was a very unfortunate accident, and could have been a tragedy, but people writing here will not affect that situation one way or another. Whether by wailing and gnashing of teeth, emoting to show our deep empathy with the child, making light to assure ourselves - well it couldn't happen to me/mine - or looking at what might be fallout if the event is used to push other agendas that have little or nothing to do with the shooting.
The best practical discussion reinforced the issue of proper gun safety - the discussion above clearly aimed the responsibility for the four rules at the adults. And you can teach some gun safety to a four year old - take a look at the NRA's "Eddie Eagle" curriculum http://eddieeagle.nra.org/
Eddie Eagle is designed for children pre-K and up (those considered generally too young to handle firearms themselves)