Ancient Greek coins
Beginning around 600 BC, each Greek city-state minted (made) its own kinds of coins (They seem to have gotten the idea from the Lydians in West Asia). A lot of the Greek coins were silver. They were made by taking a small lump of silver and putting it on an iron mold, and then striking it with a hammer that had another kind of mold in it. That way you could squash a picture into both sides at the same time.
Silver coins from Corinth had a picture of the flying horse Pegasus. Can you see him?
Just like today, some coins were worth more than others. This (below) is a smaller coin, an obol. An unskilled worker, like someone who unloaded boats or dug ditches, in Athens, would be paid about two obols a day.
All the designs on these coins changed a little from year to year, so numismatists can tell what year (more or less) a particular coin was made, or struck.
To find out more about Greek coins, check out these books from Amazon or your library:
Eyewitness: Money (Eyewitness Books) (2000).
Sold!: The Origins of Money and Trade (Buried Worlds) (1994). School Library Journal says, "Grade 6-10-Covering primarily the ancient Mediterranean civilizations, this well-written, beautifully illustrated account describes early forms of money, how the first coins were made, and what they reveal to archaeologists about the people who used them."
Ancient History from Coins, by C. J. Howgego (1995). Not for kids, but a good introduction to what we can learn about history from coins.
Greek Coins, by Ian Carradice (1995). This handbook for beginners shows some of the different types of Greek coins, with a little historical background. About a page per century.