Cain, the Human
Now, it probably didn’t take her long to figure out that Cain was no saint. His biggest claim to fame in history is that he is the first noted murderer. The kind of person who would be willing to kill his own brother over a sacrifice was probably not a model child.
Then she gave birth to Cain’s brother Abel. Cain worked the soil, and Abel was a shepherd. Besides their occupations, this pair of verses tells us that they were older, old enough to be working for a living.
There’s one other thing to note here: these are NOT Adam and Eve’s only two children. We know for sure that Cain has a wife at the time he is expelled from the area for killing Abel (later Genesis four). Since he took his wife with him, Adam and Eve’s family included at least one other woman at this time. It also seems likely there were other brothers and sisters at this time.
But, Genesis 4 and 5 are only concerned about two pieces of the story of Adam and Eve’s family: the murder, the genealogy of the killer, and the line of the promised Messiah (i.e. the genealogy of Seth, which comes in Genesis five).