Where do old lullibies come from?

i started listening to them when i had my baby 3 months ago. i have heard them all before that but now that i sing them to him i started listening to what they say and its crazy what they say.. and mean.. "ring around the rosies pocket full of poseys ashes ashes we all fall down.." weird to me.. "rock aby baby in the tree top, when the wind blows the cradle will rock, when the bow breaks the cradle will fall and down will come baby cradle in all" come on.. is this what makes a baby fall alseep? what is the logic behind these sogs..? there are many more but im sure you get the point..