Why Do SO Many Children's Nursery Rhymes End with Something Tragic?

In connection with the adult entertainment, popular theory claims that many of the nursery rhymes of today were not written for children. They were rooted in the political and social undertones of the past. Many started out as folk songs, as adult rhymes, to camouflage an unpleasant message or a distasteful event in their local history. Yet, it is possible to read into the various rhymes, connotations about Kings and Queens and social injustices. Rhymes were a sort of euphemism.