An egg-shaped figure falls off a wall and proves beyond mending, however many horses and men turn up to try. The rhyme never actually says Humpty is an egg, which is part of its long-running charm and a nice thing to let a child work out for themselves. Four lines are enough to teach the shape of a story: a fall, a failed rescue, an ending.
From Mother Goose / Nursery Rhymes (traditional). See the whole collection.
Humpty Dumpty sat on a wall,
Humpty Dumpty had a great fall;
All the King's horses, and all the King's men
Cannot put Humpty Dumpty together again.
Public domain. Text from The Real Mother Goose (Blanche Fisher Wright, 1916), via Project Gutenberg. View the source edition