Adam didn't 'know' Eve and Eve didn't conceive till Genesis 4, AFTER they were kicked out of the garden.
The Bible says they had relations after being kicked out, but it doesn't say anything about what happened before. Maybe they had relations beforehand, and maybe they didn't. There's no way of knowing. Maybe Adam was rounding third when she brought him the apple.
However, we know that God intended for them to have relations before the fall.