The bicycle thief joke, but about wagons.
I originally heard a version of this story as a bicycle thief, somebody who was bicycling over the border, probably the Mexican border given my location in Southern California, and stealing bicycles. It's kind of an old story, but personalized in this version. The characters are given personality. There are three brothers who can see really well, even with x-ray vision. The king hires them and makes them guards, and says, "They're so good that nobody can fool them. So if anybody fools them, he'll get a medal." A bunch of people try to fool them. Nobody can fool them. This little boy named Gillespie liked to play with them, but the guards decide that since they're famous they should act all serious and stop playing with Gillespie. He's sad, so he wants to fool them. He takes a bunch of wagonloads of stuff out, and they look through the piles of sand and leaves, and write down what he takes out in the wagon, and they fail to write down the fact that he took the wagons and he's got a bunch of wagons at home and he gets a medal and everybody laughs because they've been fooled and it's funny.
Strangely, in a book about seeing small details, there's a couple of typos. Like, on the third day he takes home some stones, and the guard says, "You're foolish to pull a pile of stones all the way home when you can find all you want right on you're own block." Also, later when he tells the king that he succeeded in fooling the guards, the king is holding a book that says "Royal Gaurd Book."
It's silly. The illustrations are dated but good. There's not much to it.