I believe God has an age of accountability for children that only He knows. Infants are not held spiritually accountable for sins since they have no knowledge of "their right hand from their left". All die physically in Adam, including infants.
But there is a difference between spiritual death and physical death.
Exactly, this is why Paul could say he was alive without the law once. If a man is born spiritually dead Paul could not have said this. Paul said when the commandment came, sin revived and he died. The law was given around 1500 years before Paul was born, so the only reasonable explanation is that he was speaking of being a child, unaware of the law and consequences before God. When he matured and understood the law, he was convicted by it and spiritually died.