I'm about to do it again.
>>an infant is an empty vessel to be filled.<<
We are not born "sin neutral". We are born sinful and fallen creatures - every one of us - since Adam. David speaks of this flowingly in several of the Psalms.
No one has to teach a child to reach for a toy and say "MINE!". No one has to teach a child to cry and fuss when he doesn't get his way. People hate hearing that their children are little sinners, but it's the Biblical truth.
There are none righteous, none who seek God. We are all born at enmity with him. Romans is very clear on this.
Here's a perspective for you... What Christ did on the Cross was the culmination of the Marriage Feast of the Lamb begun during the Last Supper. In this celebrated liturgy, we were brought into the family of God as Christ's bride, the Church. The ritual and realities conform to ancient convenant ceremonies where families were formed. It is more than pardon, it is adoption.
In Baptism, we are washed clean and we take on God's Name as a new creation (we are Baptized in the Name of the Father, Son and Holy Spirit). Just as the neighbor kid can't become a member of my household on his own, we couldn't become members of God's family without Him covenanting with us. There is no reason that the infant that Christ said should "come to" Him, can't be born again into this reality of God's family just as the infant was to be circumcised in the old convenant to be a member of God's Holy People, Israel.