Infants can't make the choice to be a follower of Christ. That's the only reason I have a problem with infant baptism. I was baptized at one month in the Episcopal Church. Years later I was immersed and it made me realize that satan could no longer hold my past against me. It was immersed in that water! We dedicate infants in our church but don't baptize them. We're to believe and be baptized. Not the other way around. It is a commandment, not a rite of salvation as many have been taught.
Actually infant baptism has a much more interesting past.
The early churched princes believed that dying without having been baptised denied one entrance to heaven. Rather than chance they might fall out of the saddle and hit their heads fatally on a rock prematurely, they opted for infant baptism.
This led to another problem, though. Sins, they believed, committed after one was baptised were mortal, sending them to hell.
Damned, literally, if you do and if you don't, they conjured up Limbo. Now, the post-baptismal sins could be worked off, giving infant baptism the go-ahead while still living the good life. Jesus could not be reached for comment.
Lutherans, on the other hand view Holy Baptism as a sacrament, a work of God, not of man. In Holy Baptism, the baptized person is cleansed of Original Sin, given the name of Christ, and taken into the Body of Christ. Babies are baptized because they are part of the "all nations" quotation in the Bible (Matt. 28:19), because Jesus invites little children to come to him, because as sinners, babies need what Baptism offers, and because babies indeed do have faith (John the Baptist had faith even in his mother's womb when he leapt in response to the visit from Mary). No one can show that babies can't have faith just because babies can't speak, and we can't read their minds, for instance, and faith is not an intellectual exercise, in any case. The Bible speaks of whole households being baptized with no indication that babies and small children were left out.
The Lutheran position is that faith is not a choice by man (no matter how many people tell themselves that they have made this "choice") but a gift from God and that God gives this gift, along with cleansing from Original Sin, in Holy Baptism, and God wants everybody to have this gift, not just grownups.
Lutherans also, would not re-Baptize. If Baptism works, it works. Getting re-Baptized indicates one believes that it didn't work the first time. (Lutherans will baptize if the person is not sure he/she has ever been baptized, however.) If Baptism is indeed God's work rather than man's work, it works every time and on everybody, not just grown-ups, and no specific amount of water is needed; given that "Baptism is the water included in God's command and combined with God's Word" (from Luther) any amount of water is sufficient because it's the Word in the water, and not really the water itself which is significant.