Each Greek city made its own silver coins, and they made them to look different from each other so you could know right away which city the coins were from. Greek minters made coins by putting a blank coin on a metal stand and setting a metal punch (like a stick as big around as one coin) on top that had the image carved into it, and then hitting the metal punch with a hammer to drive it into the coin and transfer the image.
You can make your own Greek coins out of clay. These Athenian coins have the owl of Athena on them, and they say “ATHE” in Greek letters. These were made by laying thin strips of clay on top of the coin, but you could also try carving a punch out of wood and using that to make the image.
Ancient Greece!: 40 Hands-On Activities to Experience This Wondrous Age (Kaleidoscope Kids), by Avery Hart, Paul Mantell, and Michael P. Kline (1999). Gives ideas to get kids thinking, rather than step-by-step instructions.