You are, no doubt, referring to Genesis 6:1-4 in your question. Let’s read that interesting passage: “Now it came to pass, when men began to multiply on the face of the earth, that the SONS OF GOD saw the DAUGHTERS OF MEN, that they were beautiful; and they took wives for themselves of all whom they chose. And the LORD said, ‘My Spirit shall not strive with man forever, for he is indeed flesh; yet his days shall be one hundred and twenty years.’ There were giants on the earth in those days, and also afterward, when the sons of God came in to the daughters of men and they bore children to them. Those were mighty men who were of old, men of renown” (NKJV).

Before we seek to answer your question, it should be noted that this passage is one of the most controversial passages in Scripture among Bible expositors. There are those who strongly disagree with the view that the “sons of God” are fallen angels who left heaven to marry human women (the “daughters of men”) and that children were born to them. Their main argument (in addition to being repulsed by the thought of angels having sexual relations with women) is that we are told in Matthew 22:30 that in heaven people will “neither marry nor are given in marriage, but are LIKE THE ANGELS OF GOD IN HEAVEN.” According to them this teaches that angels are SEXLESS and DO NOT MARRY. This is TRUE OF ANGELS IN HEAVEN, but in Jude 6 we are told of “angels who did not keep their proper domain, but LEFT THEIR OWN ABODE.” So, it is conceivable that Jude is writing of the “sons of God” (a phrase which was only used of ANGELS in the Old Testament…see Job 1:6 and 2:1) WHO LEFT HEAVEN to enter into an unholy and unnatural union with human women. In fact, Jude goes on to describe their sin in verse 7, “AS Sodom and Gomorrah, and the cities around them in a SIMILAR MANNER TO THESE, HAVING GIVEN THEMSELVES OVER TO SEXUAL IMMORALITY AND GONE AFTER STRANGE FLESH.” The sin of the fallen angels was sexual immorality and unnatural, just like the sin (of homosexuality) in Sodom and Gomorrah (see Genesis 19:1-5). It is also said by those who oppose this view that ANGELS ARE SPIRITS and thus they cannot have sexual relations with women who have a physical body. But Scripture teaches us that angels can assume a human form at times (see Genesis 18:1-5 and 19:1-5).

Regarding your question, it is obvious that the children that were born as a result of this unholy and unnatural union were abnormal, to say the least. They were called “giants” which is the Hebrew word NEPHILIM, meaning “fallen ones.” Can we actually say they were “half angel/half man”? It would seem so, for the word “Nephilim” calls attention to them being “fallen angels,” but they are also called “MEN of renown,” which speaks of them as being “men.”

Will those children stand before God on Judgment Day? I don’t know that we can say this with any certainty, for Scripture only speaks of mankind having to stand before God to face His holy judgment at the Great White Throne Judgment (see Revelation 20:11-15). I might add that Scripture also tells us that salvation is only being offered to MEN and not to ANGELS, for after speaking of Christ becoming a man to defeat Satan and to save men in Hebrews 2:14-15 we read, “For indeed He does not give aid to angels, but He does give aid to the seed of Abraham” (verse 16). Yet even if they don’t stand before God on the last great Day of Judgment, we do know that God was so appalled by this monstrosity, along with the corruption and violence of the rest of the human race (Genesis 6:5, 11-12), that He decided to destroy everything that had life by a worldwide flood (see verses 7, 13, 17). Only Noah and his family were spared from this universal judgment (see verses 8-10, 13-22).  (366.3)  (DO)