What makes people kill children?

And more importantly, what makes me read the news items? I know that when I click one of those links I will be reading a story that breaks my heart.

Take this latest one for example, a mother in the belgian town of Angleur near Liege let's her 21 months old toddler starve to death because she didn't want the child and felt neglected by her partner who was working in another country. She calls emergency services because the child was sitting lifeless in his chair for two hours. Autopsy revealed a 0% fat content in the body. Her three other surviving children have been taken away.

Can anyone imagine the agony and despair that child must have gone trough? I've got two children, I remember that age when they'd sit in their little chairs munching their way trough a bowl of fruit.
It's bad enough that children die in famines but this....