Albert Barnes Commentary Exodus 4:20

"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." — Exodus 4:20 (ASV)

An ass - Literally, “the ass,” which, according to Hebrew idiom, means that he set them upon asses. This is the first notice of other sons besides Gershom.

The rod of God - The staff of Moses was consecrated by the miracle (Exodus 4:2) and became “the rod of God.”