Genesis 4:26 ASV, Genesis 6:2 ASV and Genesis 6:4 ASV

Like many people, I've heard of the claims that Angels, fallen from Heaven, came to Earth and procreated with the daughters of men. I'm not sure the text teaches this though. The closest reference to what we'd consider "sons of God" would be the line of Seth, who in Chapter 4 verse 26 "began to call upon the name of the Lord." Is it possible that those who once sought after God are now taking part in worldly relationships with ungodly women?