The Origins of Nursery Rhymes - What do we really know?

This morning, I saw Peter wandering around wearing only one shoe, and instantly I began quoting "Diddle diddle dumpling my son [Peter]..." That led to other nursery rhymes, and as Peter and I were walking to school this morning he commented, "That reminds me of that one YouTube video I watched."

"That one video you watched?" I blinked at him. "How many YouTube videos have you watched in your life?" I asked him.

He rolled his eyes at me. "I mean that one video that talked about the origins of the nursery rhymes. Like, did you know that Humpty Dumpty wasn't really an egg?"

"He wasn't?"

"No. It was a cannon in a war somewhere."

Interesting. Of course I knew that nursery rhymes supposedly refer to events in the past. Like Ring Around the Rosies refers to the black plague. But what do the other nursery rhymes refer to?

So when I got home, I did a bit of research. What does Wikipedia have to say about the origins of nursery rhymes?

"Many nursery rhymes have been argued to have hidden meanings and origins. John Bellenden Ker (1765?–1842), for example, wrote four volumes arguing that English nursery rhymes were actually written in 'Low Saxon', a hypothetical early form of Dutch. He then 'translated' them back into English, revealing in particular a strong tendency to anti-clericalism.[17][18] Many of the ideas about the links between rhymes and historical persons, or events, can be traced back to Katherine Elwes's book The Real Personages of Mother Goose (1930), in which she linked famous nursery-rhyme characters with real people, on little or no evidence. She assumed that children's songs were a peculiar form of coded historical narrative, propaganda or covert protest, and rarely considered that they could have been written simply for entertainment.[17][19]" (https://en.wikipedia.org/wiki/Nursery_rhyme)

Does that sound a bit skeptical to you? There follows a chart with nursery rhyme names, supposed origin, and meaning supported by evidence - which usually is "no evidence" or "unknown". There were only a couple that were supported:

"Mary Had a Little Lamb" is a relatively modern poem (1830) based on a true story. A girl named Mary Sawyer had a pet lamb which she brought to school when her brother suggested it.

Old King Cole is based on a man named Richard Cole-brook in the 17th century who was known as Old King Cole. Then again, the Wikipedia article specific to Old King Cole states "There is much speculation about the identity of King Cole, but it is unlikely that he can be identified reliably given the centuries between the attestation of the rhyme and the putative identities; none of the extant theories are well supported.[3]"

What about Humpty Dumpty? Wikipedia's article on Humpty Dumpty suggests it might have originated as a riddle. It might have been a reference to King Richard III, or to the downfall of Cardinal Wolsey, or it could indeed have referred to a cannon used in a siege in 1648. 

And "Ring Around the Rosies"? Wikipedia describes the plague interpretation as an urban legend, not supported by early versions of the poem. 

And so on, and so on. Almost everything I thought I knew about the origins of nursery rhymes was debunked and only good for throwing out the window, the window, the second story window... with a heave and a ho and a mighty fine throw, I throw it out the window.

But then again, how reliable is Wikipedia anyway? Other websites still support classical, if dark, interpretations... like this Mental Floss article. Or this one from the Huffington Post. I guess you can believe whatever you want.