Did you know that the history behind some of the most common nursery rhymes is quite dark? The history behind "Ring around the Rosie" is particularly dark. "Ring around the Rosie" is a reference to the black death (the whole rhyme is a reference to the black death tho) and how people that had the plaque would often be very pink or red due to extremely high fever induced by the plaque. "Pockets full of posies" is that the streets would be so littered with dead or dying people that people walking around would put heavily perfumed flowers in their pockets to help hide the stench. "Ashes, ashes, we all fall down." because so many people were dying they were often cremated to keep up with the people dying.
Another dark rhyme is " Mary Mary quite contrary." (I don't know as much about this rhyme so not as much info is provided) The "Mary" in the rhyme is referencing Mary I of England. "How does your garden grow." the "Garden" in this line is her kingdom.
:)