Why do so many adults kill their kids?

I was on vacation for a few days and watched a little news and it seemed like all the stories were about people killing their children.

What are your theories about how to prevent this from continuing, as a society?

One was shaken by a boyfriend.
One was given Zoloft by the mother.
One in Pleasant Hill, MO was a baby in Quickcrete in a bucket.

Here’s an interesting article-http://www.denverpost.com/ci_18151310