I recall reading some where that Ring a Roses was not about the plague, as is popularly imagined, but annoyingly can't remember more details.
See saw Marjory Daw
Jack shall have a new master
he shall have but a penny a day
because he can't work any faster
was a re-write of an older Cornish rhyme -
See saw Marjory Daw
sold her bed & laid on straw
sold the straw & laid on hay
wasn't she a dirty slut to live this way (or alternatively - then Pisky came & took her away)
I believe the rhyme was rewritten as some kind of political ditty in the 19th Century, but again I'm let down by my swiss cheese memory. If I remembered half what I once knew I'd be a genius
Could the Jack & Jill sexual connotation come from the playground corruption -
Jack & Jill went up the hill to fetch a pail of water,
I don't know what they did up there, but now they've got a daughter
I highly recommend the work of Iona & Peter Opie to any one interested in adapted nursery rhymes & playground lore in general.