How many sons does Moses have?

Exodus 4:20 says, “And Moses took his wife and his sons, and set them upon an ass, and he returned to the land of Egypt: and Moses took the rod of God in his hand.”  This can’t be right.  Moses and Zipporah only had one son so far. Exodus 2:22 says, “And she bare him a son, and he called his name Gershom”