Going from Enosh, the son of Seth and grandson of Adam, we go up to another Enoch in the family tree, namely the son of Jared and grandson of Mahalalel. We know those descendants of Adam had come to recognise the Divine Creator as their God to call upon His Name.
Elohim had blessed the human beings He had created and allowed them to have children. That way A'dham became the father "of a son" in his own likeness, "after" his own image. We were not told this about Cain and Abel simply because the text did not wish to discuss them at length. In this chapter 5 Moses goes straight to the third son of Adam, Enosh. It is noted that from that time the people started to call upon the Name of Jehovah God.
The fifth chapter of the first book of the Pentateuch brings us the accounting of mankind. Moses gives an idea how the Children of God came one after the other on earth to play their role in history.
Adam and Eve got many children and their children also gave birth to several children, so that the world was populated as God had told them.