"Sally sells seashells by the sea shore."
"How much wood would a woodchuck chuck if a woodchuck could chuck wood?"
These are all very fun & silly examples of a literary device called "alliteration", the repetition of the opening sound of words. Designed to be both tongue twisters and humorous, they stick in the mind and are a fun game for kids and elementary school English teachers.
But it should be noted that alliteration is a very useful technique, with no requirement for either twisting tongues or humor. Used properly, its a great way to (as Kris Kristofferson once put it) have words "slide off the tongue and into the ear".