Since this is child friendly, I just used red paint.
The Battle of Thermopylae
The Battle of Salamis
Persia starts a war with Greece to conquer them. Though there were many immortals (soldiers), they were still defeated because Greece had better weapons and strength. When the battle ended, a man named Pheidippides runs to Athens to exclaim their victory.
Also the Battle of Marathon
A Greek traitor named Ephialtes showed the Persian army a way to get revenge by leading them around the mountains to attack from behind.
Also the Battle of Thermopylae
During this fight, their transportation was with boats. The Persian ships were too big for the canal they were going through, so the Greeks easily defeated them with their small boats. Hence, being big isn't always good.
...Unfortunately, He dies once he finishes the task.
Still child friendly; no humans were harmed in the making of this comic.
(P.S, we couldn't afford a river with mountains around it for the Battle of Salamis because of budget cuts).