In the classic Old Testament, Eve has her first child, then her second and one (Cain) kills the other (Able). Cain is cursed to wander. Cain’s first concern thereafter is that the other humans on the Earth, not children of Adam and Eve, will kill him as he wanders. The Pearl of Great Price does give us a different source for those humans. However, later, Noah’s great grandson, before the Tower of Babel, will divide the land between his brethren and the gentile peoples, according to their languages (Genesis 4:14, 10:5). Translations changes, in some editions, obscure that language. So, are we all children of Adam the same way that we are children of Abraham (i.e. mostly by adoption)?
It gets better in Genesis 6:4. Nephilim were on the earth before and after the flood. See also Numbers 13:33. Reading context, translator notes and older traditions makes the point very clearly. There appear to have been no Nephilim on the Ark. Which fits with the dividing the land with the gentiles, “everyone, after his tongue.”
Which makes for interesting implications. What other survivors were there outside the Flood? The Nephilim, the gentile nations speaking other languages, all the fish (salt and fresh water — no fish on the Ark, just FYI), there is a lot to think about there.
But better, lots to speculate about!