Focusing on the friendship between Gilgamesh and Enkidu and the journey that Gilgamesh takes to find the secret to eternal life is the best way to adapt their story for children. This removes a great deal of the violence and rape from this ancient Mesopotamian epic.
When Gilgamesh first became the king of Uruk, he was cruel, taking any woman whom he wanted sexually at any time and forcing his subjects to perform slave labor on an elaborate series of construction projects. The gods decided to create Enkidu to temper Gilgamesh's arrogance, and after Enkidu stopped Gilgamesh from raping a woman on her wedding night, the two became friends and went on an adventure. Their friendship is a great starting point for an adapted story for children.
Enkidu and Gilgamesh fight the Bull of Heaven, which the gods had sent as punishment when Gilgamesh rejects the romantic advances of Ishtar, the goddess of love. Children will appreciate the two men fighting the bull, although they might not understand the reason for the bull's arrival. The gods are angered when Gilgamesh and Enkidu kill the bull, and so they choose Enkidu to die.
Gilgamesh goes into the underworld to find the secret of eternal life by visiting Utnapishtim. Utnapishtim points him to a plant that restores youth. Gilgamesh takes it with him, but a snake steals it while Gilgamesh is taking a bath in a small lagoon, and he returns to Uruk broken-hearted, accepting his mortality. Children can understand the frustration that would go along with losing the plant, even if they are not yet sure what mortality is.