What you are saying is so ridiculous that I almost do not want to respond. Paul may have been dealing with a specific issue in the Church at Rome, but his statements were universal when he said, "… For we have preciously charged both Jews and Greeks that they are ALL UNDER SIN. 3:9. Then he quotes from Psalms 14 when he said, “… there is NONE who does good, NO NOT ONE.” Ro. 3:12 These are all general in nature and apply to anyone and everyone.
Look,… Adam and Eve were NOT born sinners. But when they sinned, they became sinners and plunged the race into the potential to sin, so that man became unable to NOT sin.
We, today are not born sinners, but once we come to the understanding of right from wrong, and then choose to do wrong, we (then) become a sinner. The pathway to becoming a sinner is by our tree of knowledge of what is right and wrong. Paul said that the natural man is “without excuse…” Ro. 1:20.
Babies, on the other hand, and the mentally impaired who do not have this KNOWLEDGE or the capacity to have knowledge of good and evil, remain in a state of sinless-ness. Their ignorance or simple inability to understand right from wrong, keeps them from becoming GUILTY.
Jesus said it this way: “I came into this world for judgment, in order that those who do not see will see, and those who do see, will become blind.” v40 Some of the Pharisees who were with Him heard these things and asked Him, ‘We aren’t blind too, are we?’, v41 If you were blind, Jesus told them, 'you wouldn’t have sin. But now that you say, ‘we see’ your sin remains." John 9:39-41
The entrance of sin comes from the knowledge of sin, not simply being born physically. Paul said it this way, "… by the deeds of the law no flesh will be justified in His sight, for by the law IS THE KNOWLEDGE OF SIN. Ro. 3:20
Secondly, new birth, for an infant is impossible. Why? Because new birth comes by hearing and understanding and accepting the word of God. see the writings of your first pope in 1st. Peter 1:23,
"having been born again, not of corruptible seed but incorruptible, THORUGH THE WORD OF GOD which lives and abides forever. " Babies do not have this capacity to understand the concepts of the salvation message found in the scriptures.
If your god will sentence a baby to the fires of hell, simply because he/she didn’t make it to the altar of baptism … a baby that knows nothing about right and wrong, a baby who does not even have the capacity to know right from wrong, … then you can keep that god. That god is not the god of the bible anyway.