It all boils' down to intent, in any case. Let me put it this way; It's tragic that this mother was killed. It's tragic anytime someone is shot and killed, whether it's a family member, friend, or complete stranger. However, the firearm was simply the tool or the way used. I pick up the local paper on a Saturday or Sunday morning, and see a total death toll 5-10x as great simply from Drunk Drivers. Yet, the restrictions' on buying Alchohol pale in comparison to those related to firearms' ownership. Timothy McVeigh killed dozens, yet how hard is it to buy either Diesel Fuel or Fertilizer?
It's a sad time for those people, and I hate to turn this into a political rant in that aspect, but...Honestly, the biggest mistake here that these people might have made, was simply raising their child properly. Until we know more about they're background, it's hard to say where the problem stems. But IMHO, they did something wrong, if it get's to the point where a child commits pre-meditated murder.