As a parent, I am genuinely staggered that more people don't kill their own kids, given how many emotionally fragile people we know there are around. There is no greater provocation to violence than a small, whining child.
Society's response to needless loss of life should always be draconian. I see hundreds of people yapping into their mobiles while driving, even when negotiating roundabouts for God's sake. When they career into pedestrians and kill them then they should be treated harshly if only to signal to others that this behaviour will not be tolerated.
But you haven't 'killed a kid'. A kid has died as the culmination of a set of decisions and random circumstances - none of which was taken with the intention of killing a kid. However, they might just as easily have not culminated in any such outcome. That to me seems highly significant from the perspective of moral guilt.
Of course you're right. The law is also there to make examples of people who break it with dire - albeit unintended - consequences. It is also there to be seen to be done. Those things are important from a societal point of view, of course, but they have nothing whatsoever to do with ethics.