Mental_Floss has compiled a list of the possible historical origins behind ten classic nursery rhymes.
5. Jack and Jill has so many interpretations, it’s hard to pick just one. I kind of like the one that says Jack and “Gill” are units of measurement. King Charles I tried to change the taxes on liquid measures so that people would receive less but be taxed the same. A “Jack” was a half pint and a “Gill” was a quarter pint. Another interpretation suggests that Jack and Jill actually represent the beheadings of Louis XVI and Marie Antoinette, which makes sense – “Jack fell down and broke his crown and Jill came tumbling after,” until you recite the second verse to the rhyme. Louis XVI definitely did not get up and trot home “as fast as he could caper; and went to bed to mend his head with vinegar and brown paper.”