Seth?

Chapter 5 of Genesis is the book of generations of Adam.  It begins with the creation of Adam.  Not even mentioning Eve, it says Gen 5.3 "and begat a son in his own likeness, after his image; and called his name Seth."  What happened to Cain and Able?  Aren't they the first born of Adam and Eve?  Now this is the third retelling of the whole creation story and the second mention of the he/she thing.  Any time you tell something three times things can get switched around, but I thought this was the perfect word of god?