I don’t know about the sin nature thing, but what boy was these verses talking about?
Isaiah 7
13Then Isaiah said, “Hear now, O house of David! Is it not enough to try the patience of men? Will you try the patience of my God as well?
14Therefore the Lord Himself will give you a sign: Behold, the virgin will be with child and will give birth to a son, and she will call Him Immanuel.
f 15By the time He knows enough to reject evil and choose good, He will be eating curds and honey.
16For before the boy knows enough to reject evil and choose good, the land of the two kings you dread will be laid waste.