... or were Cain and Abel their first, after getting thrown out? There seems to be some who think they had lots of children while in the Garden, and lots after they were tossed out, and those who think they didn't have any until they were tossed out. I've only read a little on this but it seems Genesis is vague enough to allow for believing they did have children before the exile.
They may think, but based on what?
First talking point made is Genesis 1:26. Note that it says 'Let
us make Man in Our image,...", implying there are multiple entities making Man, then the story reverts back to the singular reference to God in the very next sentence, re Adam and Eve, which can be taken as more than just Adam and Eve may being created here, then in 1:28 he exhorts them to 'be fruitful and multiply'. The Fall of Man doesn't come around until Chapter 3. Chapter 3:16 also implies childbirth was painless before the Fall, so why mention it was now painful if Eve wouldn't have known either way if she had never had children before?
So the narrative goes. IMO it could be read either way, and doesn't specifically state one way or the other, but it's vague enough to allow for there being children in the Garden.