Why do we baptize small children?
In short: We baptize them because baptism is not a diploma you get when you are grown up and understand everything; it is a new birth, an entry into God's family. You don't wait for a child to grow up to love or feed them, you welcome them while they are small. Likewise, the Church does not leave the little one on the doorstep, but takes them in its arms from the very beginning.
The Orthodox nuance
The objection comes mostly from some Protestants, such as Baptists, and it is honest: they say you must first believe, then be baptized, so baptism should only be for adults who confess their faith. They have a point; in the New Testament, we see many adults baptized after believing, which is natural since they were just turning to Christ.
But the Church has baptized children from the beginning, and she has foundations for this. First, in the Acts of the Apostles, "entire households" are baptized, families with all they included, most likely children too. Then, Christ Himself says: let the little children come to me, and do not forbid them (Mark 10:14). If the old covenant welcomed infants from the eighth day through circumcision, how much more does the new covenant not leave them outside.
And this is tied to how we understand salvation. If baptism were merely a sign of my faith, then yes, I should wait. But if baptism is truly a healing, a grafting onto Christ, a birth of water and the Spirit, then why delay it? The child is not saved by his developed faith; he is carried by the faith of the Church, of the parents, and of the godparents, who commit to raising him in Christ. He then grows into what he has received.
Sources
- Mark 10:14 (let the children come to me)
- Acts 16:15 and 16:33 (baptism of entire households)
- John 3:5 (born of water and the Spirit)
- Colossians 2:11-12