A tiny four-line rhyme built almost entirely around its own rhythm and the fun of the name Robin-a-Bobbin. The archer's aim goes wrong in the last line, which is the joke, though it does mean a crow ends up shot.
From Mother Goose / Nursery Rhymes (traditional). See the whole collection.
Robin-a-Bobbin
Bent his bow,
Shot at a pigeon,
And killed a crow.
About this rhyme
A short nonsense rhyme built on a joke about bad aim: Robin bends his bow at a pigeon and hits a crow instead. That's the whole rhyme, over almost as soon as it starts, which makes it a good quick one before moving on to something longer.
Public domain. Text from The Real Mother Goose (Blanche Fisher Wright, 1916), via Project Gutenberg. View the source edition