In Genesis 4:1, Adam “knew” his wife and she bore Cain. (NAB translation, “had relations with”).
In Genesis 6:4, the sons of God “came in to” the daughters of men, who bore them children. (NAB translation, “had intercourse”).
Both translations appear to show a difference in relationship. The sons of God appear to be merely using their partners for physical pleasure, rather than engaging in a rightly ordered marital union.