Shel Silverstein has a great poem about money on page 35 of his book Where the Sidewalk Ends. The poem is called Smart. You can find it on Amazon, most book stores, or your local library.
A kid gets some money and makes trades with various people each time he thinks he is getting the better deal. But he doesn't understand the value of the coins, he just knows that he has more actual coins than he started out with.
Using this Poem with Kids
This poem is intended for kids who actually understand the value of money. Some kids have this mastered in Kindergarten, while others may not truly understand the humor until third or fourth grade. But even junior high kids will smirk at the silliness of "little Kids."
Use real money as a demonstration while reading the poem through to give kids a visual of what is happening in the poem.
For early and middle school, you could figure out what they should have traded, and how he could have ended up with even more money.
Try to figure out who got the "best deal" out of all the trades.
Use this as a jump start for talking about why we have multiple coins in the first place. Hat would happen if we only had pennies, or dollar bills, how would that change the way we did business, or carried our money around.