Did anyone bother to look at the fake gun the boy had? It is a replica (they shouldn't even make these things) of a semiautomatic and the orange tip to set it apart was removed. It looked real. In a short blip of time where someone had to make, what they believed was a life or death call, one could not determine off the cuff that it was fake as it looked more real than fake. As for blame, there may be plenty to go around. How about the parents for letting him play with such an item? Especially when it looked the way it did? Yes, the boy as well, for waving what appeared to be a real gun at people, and this also falls back upon the parents for not teaching him well. Perhaps the dispatcher did transmit the information about the gun possibly being fake, perhaps they didn't, but the officer on the scene had to make the actual determination that is was fake and that couldn't be done in a glimpse, especially given what type of fake gun it was.
All that said, is it horrible that a 12y/o boy died because of all this? Of course. But I can't possibly just put the blame for that on the officer, not with actually seeing the gun the boy was waving/holding and appeared to pull upon the officer. 12 y/o kids and younger have been known to commit brutal crimes. So his age is not a defense against the officer either.
The one thing I will comment upon here is that I believe that officers could be trained in better take-down and shooting efforts. If they are going to use a gun to take down a suspect then they better have better capabilities with aiming and aim for extremities, not center mass. Take out a leg if possible. Center mass should only be used if in an actual fire fight. JMO