For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
Paul states that "through one act of righteousness there resulted justification of life to all men." Rom 5:18 "All men" is a universal statement. Christ's legal justification of all men in Himself is not the limited atonement of Calvinism. The latter is "another gospel".
Christ has saved "all men" in Himself. If men are justified by faith then "faith" becomes the Savior, not Christ. Hence the gospel is that every conceived human comes into this world "justified unto life". Christ has legally redeemed the world in Himself.
Now, when and if one reaches the age of accountability, he/she is under obligation to accept what Christ has already done in Himself through faith. Faith is accepting the good news. Those who reach the age of accountability and reject the gospel will remain under law and its curse. They will not inherit the kingdom of God.
All babies who prematurely die or are murdered (such as abortion) will be in heaven. Christ in His love has taken care of the most vulnerable.
I would like to clarify my following statement: "...There is a difference between transgression, which requires a knowledge of the law, and being born a sinner. Infants are sinners just not guilty sinners. They stand condemned, not because of transgression, but because they share in Adam's fallen life."
Please go to Romans 5:12. I will use the NASB.
12 "Therefore, just as through one man sin entered into the world, and death through sin, and so death spread to all men, because all sinned— "
Through Adam sin entered the human race (i.e., our humanity) and the wages of sin is death (see Rom 6:23). Adam's sin was a corporate sin because all men were biologically in him when he transgressed. See Acts 17:26: "He (God) made from one man (Adam) every nation of mankind." Simply put we are multiplication of Adam's fallen, sinful life.
Verse 13 "For until the Law sin was in the world, but sin is not imputed when there is no law."
Why was the fallen human race between the fall of Adam and Moses (where the law was given) dying? The law had not been officially given on Mount Sinai and Paul tells us that "sin is not imputed when there is no law". He repeats this in Romans 4:15 "The Law brings about wrath, but where there is no law, there also is no violation."
So the human race between Adam and Moses (where the law was posted) were dying, but not because they were guilty of transgression. They were condemned because they all shared Adam's fallen life indwelt by iniquity.