First off Liver: Thank you for your service.
Having more information, and the actual image from the reporter's camera, I can see why they needed to react quickly. With the insurgent attacks, being a threat, and clearly a LOS to the military vehicles, by a possible RPG, I can understand fully how they would make the mistake.
I don't fault them for the "callousness" because honestly, what do you expect them to do... cry because they accidentally hit a child. They have to stay sane somehow. If they let every little thing hit them and eat at their conscience, they would be eating a bullet. They have to keep their wits about them or more people will die. Worry about that stuff when you aren't in a hostile environment. But don't let it tear you up.
"I would rather be exposed to the inconveniences attending too much liberty than to those attending too small a degree of it." Thomas Jefferson