“And the angels, which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day.
Even as Sodom and Gomorrah, and the cities about them in like manner, giving themselves over to fornication, and going after strange flesh, are set forth for an example, suffering the vengeance of eternal fire” (Jud 6 & 7).
“For if God spared not the angels that sinned, but cast them down to hell, and delivered them into chains of darkness, to be reserved unto judgment” (2 Pet 2:4).
“That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose.
There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bear children to them, the same became mighty men which were of old, men of renown” (Gen 6:2 & 4).
Note: It is possible for angels, fallen or not, to impregnate a human, but it is suspect. Simply because angels do not have sex organs (Matt 22:30).
A demon, or many at one time, can enter a person’s body (Lk 8:29-30), so it is possible that they entered a man and when he impregnated the woman the demon’s stature affected the size of the birth.
I have nothing to base this one, this is just a thought.