David's son, who was a result of David and Bathsheba's adultery, died as an infant and David acknowledged that he wouldn't see his son again until heaven. In other words God did not hold his son accountable for his sin nature, when he had not yet had a chance to reject God.
Our eternal destiny is the most important decision of our lives. The Scriptures present us with a perfectly just and fair God. Having a sin nature gives us a propensity to sin. The only sin that can condemn us is the rejection of God's pardon for our sin.
According to the Bible, God gives each of us enough information about Him, that we can make our own decision to follow or reject Him. We are all on death row awaiting death. God has offered us all a pardon for our sins, and removal from death row. All we must do in order to receive the pardon is acknowledge we are on death row and in need of a pardon, then accept the pardon that God has provided. Looking to the death and resurrection of Jesus Christ for salvation. When we do this, we are immediately released from the prison of our sin, which had condemned us.
Noah and his family were the only people on the planet who did not reject God. The rest of civilization experienced simultanious ushering to the final judgement of God for rejecting Him (there may have been children who went straight to heaven, their temporal lives having been cut short by the curse of sin -- as was David's son and the people in the Tsunami -- which brought on the flood). Physical death marks the end of our opportunity to make a choice. Choosing to accept the pardon naturally changes one's perspective on physical death.
Why is rejection of God's pardon of our sin a sin? What is sinful about that?
Why do we need pardon for behavior which is an unavoidable part of our nature?