One: He wasn't playing with a toy gun. He was pointing a realistic looking replica gun at people in a public place.
Two: We don't know anything about the kid. Some 12-year-olds look ten, some look as old as eighteen. Unless we see a picture of him at 4'6", we can't assume he actually looked like a kid, and it's not like he was running around with his age clipped to his shoulder.
Three: He ignored an armed police officer's directions and instead reached for what everyone in this thread will agree looks startlingly like a real god-damned weapon.
This isn't about some white cop being afraid of black kids, it's about a police officer responding to a situation exactly as he was trained to do, because the officer quite reasonably concludede that he might about to be shot based on the evidence in front of him.
All dispatch knew was that the gun might be fake, and the suspect might be a kid. For all the officer knew, it was a short adult, the gun was real, and the suspect was on some kind of drug.
The logical result of this story shouldn't ever be "Cops hate black kids and want to shoot them", but "Giving children access to fake replica guns and not educating them about handling them responsibly is a terrible god-damned idea."
Edit: Also, as an aside, assuming this is a racial thing is just.... Gah. Way to turn a senseless tragedy into a political talking point. Good job.
It's stated in the 911 call.