Please allow me an opportunity to respond to your following statement:
It is incorrect to start with the premise that infants are born "dead." They are born with a sin nature, but they are not born dead. God does not impute sin to an infant, or to anyone else who cannot comprehend the fact that they are guilty before God.
I think it is without question that every human being born with life is born alive. However, there is a difference between those who are 'physically' alive and those who are 'spiritually' alive. I agree with you that all babies are born with a sin nature, however, the fact that they have a 'sin' nature logically (and Biblically) concludes they are conceived, born and alive in the condemnation of sin. Why else would they have a sin nature if their nature is not immersed in 'sin' which is a transgression of God's law, be it commission or omission?
Our sin nature is the non-presence of spiritual life, proven by the fact that unless we receive spiritual life (clearly meaning we don't already have it) we will never see the Kingdom of God. We must be born-again. The term 'born-again' clearly assumes that life already exists but there must be another type of life that must be born-again (from above) or we shall all perish. John 3:16 plainly states that those who 'have' eternal life will not perish. Now, it must be obvious that if we are perishing without eternal life, we must have eternal in order to not perish. So, either all babies must receive eternal life or they will all perish. There is no difference between their need for eternal life and an adult's in order to not perish. John 10:28 states Christ 'gives' eternal life to those who will not perish. 1 Cor. 15:50 concludes this line of reasoning by simply stating that "[i]flesh and blood cannot inherit the kingdom of God[/i]", even though there is 'physical' life in both the flesh and blood.
God has imputed sin to all who are conceived in sin. So, unless you are willing to state that babies come into this world in sinless perfection, then they obviously are conceived in sin as stated in Psalm 51:5, which doesn't mean the Mother was sinning at the moment of conception. And if they have a 'sin' nature, they are obviously not conceived without inheriting the wrath of God upon them which necessitates even their need for a 'spiritual' re-birth in order to see/enter the kingdom of God.
Nowhere does Holy Scripture even remotely suggest that God does not impute sin to anyone who can't consciously understand the matter of sin. If you know of any such text, I would love for you to present it.