A couple things here. I actually don't blame anyone but the 911 dispatcher. It's really a ****** situation.
1) It appears that the gun wasn't Tamir's, but a friend's toy gun, given to him to play with not long before 911 was called. So I protest the idea of "****** parenting" being the problem here, if that's true.
2) The 911 caller told the dispatcher that Tamir "was probably a juvenile" and was holding "probably a toy gun." It seems the 911 dispatcher did not relay this information to the cops, so what they had was probably something along the lines of "suspect waving gun at people in park."
3) I don't know how far cops are supposed to pull up to suspects with guns; maybe it is farther than that. But Tamir Rice, while just 12, was 5'7" and 195 pounds, so he didn't necessarily look like a child. If I'm a cop, and I pull up towards a suspect, and he picks up a gun off the ground, puts it in his pants, and starts walking up towards me, when I tell him to put his hands in the air, and he reaches his for gun, there's a very good chance I'm shooting him, and I'm thinking that's justified.