According to Josephus, a first-century Jew who was alive during the destruction of Jerusalem by the Romans, they believed angels had children with human women.
"For many Angels of God accompanied with women, and begat sons that proved unjust, and despisers of all that was good; on account of the confidence they had in their own strength. For the tradition is, that these men did what resembled the acts of those whom the Grecians call Giants."
Something to consider:
THE MEANING OF “SONS OF GOD” IN GENESIS 6:1-4
https://www.friendsofsabbath.org/Further_Research/Miscellaneous/Sons-of-God-in-Genesis-6.pdf