It depends on extenuating circumstances. Personally, I'll cut a "child" a lot more slack than I would a teenager. In fact we've got a twisted on going on right now. My little niece's (8 years old) "boyfriend" got a hold of a locked and loaded gun from his buddy's house. Pointed it at his sister and shouted "bang" hitting her in the arm. The kid panicked and ran off, leaving his sister to bleed to death. It's a horrible, terrible accident. But justice has to take accidents into consideration. Nobody is even considering charging the boy. To the point that the "official" record is she shot herself with a gun he brought over. The local towns are practically burning both sets of parents in effigy for their failures. One for failing to teach their child that you NEVER point a firearm at another human being and the other for leaving a freaking loaded weapon with the safety off just lying around.
Now, had the kids been older, say 14-15 and had shot his sister because she had annoyed him. That would have been different. As someone with that though process is a danger to society and needs to be as far away from society as possible.
I am 45, but I am not to old to remember how fucked up it was being a teenager. To say that they should be expected to have the judgement and restraint of an adult is to belittle the turmoil they are experiencing. Teens are wrestling with the loss of youth and the expectations of maturity. It's all very disorienting. I would totally cut them slack, and again where are the parents of these teens??? Why aren't they responsible. It takes a very disturbed person to kill somebody. You think parents would notice.