I opened part 4 of this series saying that who we baptize should depend on what the Bible teaches about what happens in baptism. So, based on the Biblical teaching that in baptism God washes away sin, connects us to Christ, and saves, who then should be baptized? The answer seems quite simple. We should baptize anyone who needs sin washed away ... anyone who needs to be connected to Christ ... anyone who needs to be saved. In other words, we should baptize everyone. After all, the Bible teaches that we are born in the image of our sinful parents (Genesis 5:1-3 and Romans 5:12-21) and Paul writes that we are by nature objects of wrath (Ephesians 2). Over and over the Bible says that until God does something to us, we are creatures of God, but not children. This means that all people need their sins washed away ... all people need to be connected to Christ ... all people need to be saved. Now, while the theology is more important that the practice of the Early Church, it is encouraging to see that, more than likely, the practice of the first Christians reflects this theology. The following is a quote on baptism practices in the Early Church is from pages 38 and 39 in the second section of Hermann Sasse's We Confess Anthology (I've broken it up into paragraphs for your benefit):

Joachim Jeremias and W.F. Flemmington with an abundance of persuasive arguments have made it seem likely that infant baptism, which is first explicitly spoken of by Irenaeus (about 185), goes back to the time of the apostles. There it would have been practiced according to the model of the Jewish baptism of proselytes. This we know was performed not only on adults, but in the case of the conversion of whole families it was performed on all who belonged to the whole "house" and so included the children. The well-known examples of Lydia, the dealer in purple, and of the jailer at Philippi (Acts 16), who were baptized with their whole household after they themselves had come to faith, would be relevant. When Polycarp testified at his martyr's trial that he had served the Lord for 86 years, that can only refer to his membership in the church. Then his baptism would have occurred in the apostolic age, before the year 70. The assertion of Justin that in his day there were many Christians in their sixties and seventies "who had become disciples of Christ as children" can only refer to people who were baptized as children between AD 80 and 90. Of Ireneaus we have spoken already. He confesses that Christ came to save all, "all who through Him are born again to God: infants, little children, boys, youth, and men." In the church order of his pupil Hippolytus the baptism of little children is explicitly mentioned. They are to be baptized prior to the adults, and their parents or a relative are to represent them in giving consent and in the confession of the creed by speaking for them in their place. When Tertullian in his writing On Baptism explicitly opposes the custom of infant baptism, he does not speak against it as if it were an innovation. So also later when Pelagius attacks Augustine's doctrine of original sin, he lets the point stand that children also are baptized and does not contest infant baptism. Similarly Origen and Cyprian take the baptism of children for granted. Origen stated that infant baptism goes back to a tradition the apostles received from the Lord, a statement that was transmitted to the Middle Ages by Dionysius the Areopagite. Cyprian gives Bishop Fidus the well-known advice that Baptism is not to be delayed until the eighth day after birth according to the analogy of circumcision. Jeremias is right when he maintains that a later introduction of infant baptism would have provoked a profound upset in the church and would have left distinct traces in the history of the church. What we know of the history of the church indicates much rather that in the early church both forms of baptism, the baptism of adults and infant baptism, always existed side by side, just as they do today in the mission fields. This can only mean that infant baptism must go back to the time of the apostles. It would have been included in the practice of baptizing whole families to which the New Testament gives witness, even though children are not explicitly mentioned.

So, in summary, baptism isn't about our confession but God's action upon sinners in need of grace. Through baptism, sinners are bound to Christ who bound himself to us in his baptism. In baptism, God promises to be our God and to call us his children. At the same time, baptism doesn't exist in a vacuum, but should always be bound with continued instruction in the Christian faith.