Headship: the choices of leaders affect those under them
The concept of Headship is very important for understanding how judgement and justice play out in the Old Testament, and even in the New Testament. Peoples and nations are judged because of the actions of their leaders:
- In Genesis 12 Pharaoh's household is afflicted by plagues because Sarai was taken into his house when he didn't know she was Abram's wife
- Egypt is judged when the Pharaoh would not let Israel leave
- Israel is judged when David took a census (2 Samuel 24, 1 Chronicles 21)
This concept is taken up in the New Testament to explain how sin has taken over all of humanity because of Adam our father's sin, and how the obedience of one man Jesus can save us (Romans 5, 1 Corinthians 15). Original sin means that we are all tainted by sin, in need of redemption, even though a infant may not yet be capable of consciously rebelling against God. In the same way, while some Egyptians may have hated the Israelites, others would not have, and yet were afflicted by the plagues all the same. When David ordered a census there is no suggestion that the whole of Israel shared in his guilt, and yet they shared in his judgement.
So in the time of Noah, we can understand that yes, every human was a sinner, but the judgement of the flood was not a sign that every human was consciously rebelling against God. As the head of households made decisions for their families, the results affected everyone. We see this not just in those who die, but even those who are saved: it is Noah alone who is righteous (the pronoun you is singular), and so his family is saved because of him, not because they merit it themselves.
Then the LORD said to Noah, "Enter the ark, you and all your household, for I have seen that you (singular) alone are righteous before me in this generation. (Genesis 7:1, CSB)
But God judges us for our own personal sins
Ezekiel 18 is a long and detailed discussion of how God judges us as individuals. The principle is clear: God is just and judges us so that we die for our own sins, not the sins of our fathers or our children.
But we know from innumerable examples in the Bible that people do die for the sins of others. We've just seen the examples of judgement of nations for the sins of their heads. Numbers 14:18 says that God "punishes the children for the sin of the parents to the third and fourth generation".
The best way I can see to reconcile these ideas is that Ezekiel 18 is talking about our eternal judgement, not the temporal judgements and punishments God deals out. When we stand before the judgement throne of God, we will answer for our sins alone. No one will receive the eternal death of hell for the sins of another. But we can die in this life for many reasons, not just our own sins.
This suggests that even the direct judgements of God in scripture do not always imply that the judged will be eternal condemned. 1 Corinthians 11:30 says that participating in communion in an unworthy manner is the cause of many of the church being sick or even asleep, meaning dead. But this is called in verse 32 discipline, not condemnation. In Acts 5 Ananias and Sapphira die when they lie to the Holy Spirit. Does this mean they were never truly saved, or that they lost their salvation? The text doesn't directly imply that. In Joshua 7 Achan and his family is executed for disobeying the instructions of God, after first confessing his sins before Joshua and the community. We can't know his heart, but the text is not incompatible with Achan genuinely repenting, even though that does not stop the temporal punishment. God never promises to rescue the repentant from all temporal consequences for sin, and indeed even temporal punishments from God.
If you're still following me, then the answer to this question about the killing of children during Noah's flood is that they were killed because of their parents' unwillingness to repent and turn back to God, and yet this temporal judgement is not the end of the matter. They, like everyone else, will be judged on judgement day for their own sins and no one else's.