Who ever said that Cain is Adams' son and not the devil or Satan the Dragon or what ever name you want to use is out of there mind Very simply first check the Hebrew manuscripts and you'll find that Eve had twins one was Adam son. Who was able the other was Cain and further proof check Cains' genealogy you'll find Adam is not there why because he's not Cain's father
Since the author believes himself wise, I left the original note unedited.
"Now Adam knew Eve his wife, and she conceived and bore Cain, and said, "I have acquired a man from the LORD." Then she bore again, this time his brother Abel. Now Abel was a keeper of sheep, but Cain was a tiller of the ground" (Genesis 4:1-2). Notice the order: Adam had sex with his wife, as a result she became pregnant and the son born as a result was named "Cain" because the couple realize the Cain was a gift to them from God. The New King James Version closely reflects the Hebrew in this verse. Every translation says basically the same thing, so I won't bother spelling out the Hebrew for you.
It is true that some assume that Abel was a twin to Cain because there was no mention of a second round of sex and conception, but you have to realize that this is an assumption and not a necessary inference.
While it is possible for a woman to conceive fraternal twins by two different men, the Bible is quite clear that Cain's father was Adam. Nowhere in the Bible is there any indication that Satan ever has sexual relations with any human.