Yes, by the time of Moses' re-entrance to Egypt he had fathered two sons. The Hebrew speaks of them in plural in several instances, including before he went before Pharaoh.
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, KJV)
And Jethro, Moses' father in law, came with his sons and his wife unto
Moses into the wilderness, where he encamped at the mount of God:
(Exodus 18:5, KJV)
In the New Testament, we have a clear statement that both of Moses' sons had been fathered while he was in Midian.
Then fled Moses at this saying, and was a stranger in the land of
Madian, where he begat two sons. (Acts 7:29, KJV)
The oldest had been circumcised as was the practice among the descendants of Abraham. Perhaps witnessing this had been traumatic for his wife, Zipporah, because she had persuaded Moses not to circumcise the next one. When Zipporah saw the sword-wielding angel, both Moses and Zipporah knew what it must be about, because Moses had neglected to circumcise the younger son. Moses, being the head of the house, was ultimately responsible, and the one about to be punished for this neglect--and Zipporah, fearing her husband was about to be killed, and perhaps convicted of her responsibility in the matter, took it upon herself to right the wrong.
How do we know Zipporah's feelings about circumcision?
So he let him go: then she said, A bloody husband thou art, because of
the circumcision. (Genesis 4:26, KJV)
She was blaming Moses for this--not herself, not the angel, and certainly not her son, from whom the blood had flowed. And, if Moses had not heretofore done the circumcision, he was certainly not the one to have made it "bloody." But the words of Zipporah open a window into her disagreement on the issue. As we know, the Midianites were also descendants of Abraham (see Genesis 25:1-2), but they were from his wife Keturah, a separate family line, and perhaps the practice of circumcision had been less carefully preserved among them.
Until every duty had been properly performed, God could not be their protector in Egypt. Remember what happened when Achan had stolen goods from Jericho? Thirty six men of Israel died during their next battle without God's protection. Moses and his family must have God's protection as he journeyed to Egypt to face off with the enemy of God's people, and the angel had been sent to warn Moses and ensure that he was fully obedient to God's covenant law.
The KJV is translating correctly in Exodus 4:20 when it speaks of "sons" in the plural. The actual Hebrew word, בָּנָ֗יו, is plural for "sons" and singular for "his"--the possessive pronoun attached as a pronominal suffix. But the Bible tells us that Moses' sons were both born to him in Midian, so there is no ambiguity on this point.