Who were the parents of Adam and Eve's first grandchild?

We know we all came from Adam and Eve. They were created perfect with no flaws. After sinning they lost that perfection and over the generations we have gotten further from that perfect state. The law on was given by God to protect humans from what could happen if we had children with parents too closely related. There was no need for that before because they were closer to perfection. That law was given to Moses thousands of years after Adam and Eve.