It's something almost impossible to train for, more info about the "kid" would have described different outcomes. Age, green hair, race, bad neighborhood, etc,.. Was the kid 10 or 15? I've seen 15 year olds, that look like men.
Whip out an Ipod, cellphone, toy gun at a cop, and very well likely can be shot in today's world.
Tough call. I'm sure the LEO feels pretty bad regardless.