 Actual sin occurs when I break the law of God and I am accountable for that law-breaking. When I break the law of God, I bear the weight of guilt associated with that violation and I am responsible for my sin against God. But babies aren't responsible for sin in the same way that you and I are. They certainly have sin natures, we can see that, but they have no understanding of sin. So between birth and a time when a child becomes accountable or responsible for their sin, how do we account for the death of that child? How is it that death reigns over those children? It's the imputation of Adam's sin. That's the argument that Paul is making in Romans chapter five. It's the imputation of Adam's sin.