Two lines long and built for a knee-bounce: three straws propped on a staff, said to make a baby laugh and cry in the same breath. About as short as a nursery rhyme gets.
From Mother Goose / Nursery Rhymes (traditional). See the whole collection.
Three straws on a staff
Would make a baby cry and laugh.
About this rhyme
Just two lines, and that's the whole rhyme: three straws on a staff, said to make a baby cry and laugh both. It isn't a story, just a small daft image and a promise of a reaction.
Say it slowly with a tickle at the end and see if the promise holds.
Public domain. Text from The Real Mother Goose (Blanche Fisher Wright, 1916), via Project Gutenberg. View the source edition