Since God said "SURELY die" then that is exactly what happened. Their spirits died, and they were banished from Eden.
Yes. and you took it a step further, which even the RCC dared not do. You imputed Adam's sin to the human race, which means that Adam's guilt was imputed to all human beings. WHICH IS TOTALLY FALSE.
This is where your confusion begins. You think that imputed, ascribed, impacted all mean the same thing. They do not. Because of Adam's disobedience, sin and death became the CURSE of the human race. Therefore the Bible says that all have sinned and come short of the glory of God.
If all infants can die sooner or later, then all infants carry the *virus* of sin within their souls. Every human being has a sin nature. But as far as a just and merciful God is concerned, since infants and young children cannot possibly comprehend or respond to the Gospel, the blood of Christ which was shed for them also ensures their salvation. They do not need to be baptized for the simple reason that the blood of Christ has infinite value, whereas water cannot wash away any sins.