How can anyone harm a child?

It seems like all we hear on the news now a days, is about parents killing their young children. How could someone take the life of their own child? If they didn't want their child or couldn't take care of it, why not give the child to someone who would love them like one of their own. There are so many families in the world that would love to have a child of their own but they can't, and here are people killing their child because they don't want them. I think we need to stand up for the rights of children, who can't fend for themselves.