Adam Clarke on Exodus 4:20

His wife and his sons - Both Gershom and Eliezer, though the birth of the latter has not yet been mentioned in the Hebrew text. See Clarke's note on Exo 2:22.

Set them upon an ass - The Septuagint reads the word in the plural, εκι τα ὑποζυγια, upon asses, as it certainly required more than one to carry Zipporah, Gershom, and Eliezer.

The rod of God - The sign of sovereign power, by which he was to perform all his miracles; once the badge of his shepherd's office, and now that by which he is to feed, rule, and protect his people Israel.