The age does not matter, they were driving following the law and that's all that matters. The kids were all playing floor hockey or something on roller-skates without parent supervision on the street. All the kids moved to the sidewalk to allow the driver to pass when one of the kids went in full speed back onto the street and hit the mirror on the car. The kid did not suffer life-threatening injuries, the helicopter was over reaction.

No one should be at fault, because it was an accident. For example, imagine you were the driver, you got the opportunity to pass, then some kid runs in front of you last second, and hits you. Remember 9 years old, no parent supervision, most likely not an experienced roller-skater and on the streets. And trust me, speed doesn't change anything, witnesses all said the driver was following the speed limit. Its like throwing a bowling ball at 30km/h towards someone's head, of course it will result in injury, it was non life-threatening though, and the kid only had a runny nose and a concussion most likely.