The validity of the baptism of infants is often doubted by many protestants. This is largely derived from the theology of the Anabaptists, a group that rose out of the Radical Reformation. The Schleitheim Confession, an early Swiss Anabaptist creed that was written in 1527, is quoted as saying:
"Baptism shall be given to all those who have learned repentance and amendment of life, and who believe truly that their sins are taken away by Christ, and to all those who walk in the resurrection of Jesus Christ, and wish to be buried with Him in death, so that they may be resurrected with Him and to all those who with this significance request it (baptism) of us and demand it for themselves. This excludes all infant baptism, the highest and chief abomination of the Pope."
This, of course, is contrary to the teachings of Orthodoxy, which correctly teaches that infants are perfectly capable of being in the Body of Christ. As pointed out by Origen, in his Homily to the Romans, "the Church received from the apostles the tradition of baptizing infants too."
Infant Baptism as the New Circumcision
the early church often contrasted the rite of baptism to that of circumcision. In the same way the rite of Circumcision initiated one into the nation of Israel and the Jewish people, the rite of Baptism brings one into the life of the Church.
"In him you were also circumcised with a circumcision not performed by human hands. Your whole self ruled by the flesh was put off when you were circumcised by Christ, having been buried with him in baptism, in which you were also raised with him through your faith in the working of God, who raised him from the dead." Colossians 2:11-12
This line of reasoning was carried on by the Holy Fathers. For example, Hilary of Poitiers, Augustine, and Cyprian all expressed the idea that Circumcision is connected to the Rite of Baptism.
Salvific Power of Baptism
Personal Death Within Christ
The Family As One Flesh
Possible Biblical References
Though there is no direct examples of infants being baptized in the Bible, there are numerous indirect references.
"Jesus said, 'Let the little children come to me, and do not hinder them, for the kingdom of heaven belongs to such as these.'" Matthew 19:14 (Note: Christ clearly says that baptism is necessary for salvation. "He that believeth and is baptized shall be saved" Mark 16:16).
"People were also bringing babies to Jesus for him to place his hands on them. When the disciples saw this, they rebuked them. But Jesus called the children to him and said, 'Let the little children come to me, and do not hinder them, for the kingdom of God belongs to such as these. Truly I tell you, anyone who will not receive the kingdom of God like a little child will never enter it.'" Luke 18:15-17 (Note: Here the people bring their infants to the Christ in the hope that He will bless them. A blessing is understood by the Church to mean an impartation of grace. Thus, the reception of grace is not dependent on an "age of reason".)
"Peter replied, “Repent and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of your sins. And you will receive the gift of the Holy Spirit. The promise is for you and your children and for all who are far off—for all whom the Lord our God will call.” Acts 2:38-39
"When she and the members of her household were baptized, she invited us to her home. 'If you consider me a believer in the Lord,' she said, 'come and stay at my house.' And she persuaded us." Acts 16:15
"At that hour of the night the jailer took them and washed their wounds; then immediately he and all his household were baptized." Acts 16:33
Ethical Implications of Credobaptism
Origen, Homily on Romans, V:9 (A.D. 244).