If Abel and Cain were Adam and Eve’s sons, then where did Cain’s wife come from? This was a question asked of me by a friend’s child.
Cain’s wife’s parents were also Adam and Eve. Scripture records the names of three of Adam and Eve’s children (Cain, Abel, and Seth), but they likely had more children whose names were unrecorded. What you can tell your friend’s child is, “Until the human race had grown to a population large enough to make such arrangements unnecessary, God allowed brothers and sisters to marry and have families together.”