Exodus 18:3

And her two sons; of which the name of the one was Gershom; for he said, I have been an alien in a strange land:

The two sons named here were the children Moses had with his wife Zipporah. Zipporah was a Midianite, a descendant of Abraham and a worshiper of the true God. She was timid and retiring in disposition, yet gentle and affectionate, and somewhat darker in complexion than the Hebrews. Miriam despised her for marrying Moses outside the Hebrews.

Moses sent his wife and his two sons to his father-in-law Jethro for safety before he left Egypt. He sent her back to Midian while on the way to Egypt to spare her the pain of witnessing the judgments that would fall on the Egyptians. They stayed with Jethro through the deliverance from Egypt until Jethro heard of the wonderful deliverance of Israel and brought the wife and children to Moses in the wilderness. There she rejoined him with the sons. After the reunion in the wilderness she saw his strength wearing away under his burdens and made her fears known to Jethro, whose counsel brought relief, while Miriam regarded Zipporah as the cause of supposed neglect toward herself and Aaron.