One, two, buckle my shoe
Three, four, shut the door
Five, six, pick up sticks
Seven, eight, lay them straight
Nine, ten, a good fat hen
Eleven, twelve, who will delve?
Thirteen, fourteen, maids a-courting
Fifteen, sixteen, maids a-kissing
Seventeen, eighteen, maids a-waiting
Nineteen, twenty, my stomach’s empty
It dates back to the Middle Ages, and several lines have very macabre origins. (What nursery rhyme doesn't?) I can also understand every word in the poem save one: "delve". This is quite rare considering the other nuggets I've seen from the period.
I went to Dictionary.com and was given the following definition: "to carry on intensive and thorough research for data, information, or the like; investigate."
I don't know much about the Middle Ages, but I'm fairly certain that children of that time period likely would not spend great amounts of time researching data.
The second definition was a little more helpful: "to dig the ground, as with a spade."
This fits with the macabre references, and is also listed as the 'Archaic' definition (commonly used in an earlier time but rare in present-day usage). Huzzah! Mystery solved. It's about digging. Grave digging to be precise...[shudder].
Now if we could just do something about that last "rhyme"...
How about Nineteen, Twenty, my eyes are squinty?