Why are the old children's songs and lullabies so morbid and violent?

I actually wrote an abnormal psychology paper about this in college, wish I still had it for reference. According to a book that I used as my source, fairy tales were never meant to be soothing and fun for children. Fairy tales were created in order to teach children life lessons at an early age. Fairy tales were suppose to search as bedrock for the child's moral development, therefore they may come off as harsh to us today given the sheltered nature our society has created for children. My paper was about how these tales can actually have an adverse effect on the children, creating psychology problems instead of enriching the child's moral development. I've posted some book titles below for further reading on the topic. I only used the Intro. to the psy. of fairy tales for my paper but I can't find the other book that I used.