Why is most child murder not in the news?

Emily Bazelon says this about the Newtown, Connecticut mass murder:

They could be us, and we could be them, right? It was so easy for me at least to feel that way, looking up Newtown’s suburban demographics: Family median income $100,000 a year, almost half the town families with children, nearly three-quarters married couples. I don’t live in the suburbs, but I live in a small-city neighborhood filled with two-parent families about 45 minutes from Newtown, and I have a son in elementary school. That was more than enough to share in the chill that spread through the country Friday. I wish I identified as much with the families of drive-by shootings of children in my city, but I don’t. I use class and, I’m sure, race to distance myself. That doesn’t work this time though.

Based on a quick Google search, well over 1,000 children are murdered in the US every year, and somewhere between 3,000 to 5,000 children are killed by guns every year. (It's not surprising that the second statistic is much larger than the first — accidents and suicides are more common than murder.) How does the media decide that 20 children killed are more important than thousands of other children killed? Of course, what happened in Newtown was especially horrific because of the large number of children who were killed all in the same place and at the same time. But how much less horrific is the murder or reckless killing of one child? In the latter case, the pain may even be compounded by the realization that it isn't considered "news."