Why Does the Catholic Church Baptize Babies?

A fair question.  The easiest and perhaps best answer would simply be that this was the constant Tradition or teaching of the early Church, right from the time of the Apostles.

Despite this, the first objection often is that babies cannot personally make the commitment necessary for Baptism.  But, since the time of Abraham right to the present, Jews have circumcised infants and brought them into the Covenant on the eighth day after birth, based on the faith of the parents, just as we do now in Christian Baptism.  Could you imagine the Apostles standing before the Jewish crowds, announcing the New Covenant, but adding that their children were excluded, until they could make the decision for themselves?  It would be unheard of!

And Scripture is very clear that the faith of a believing parent or spouse can have great effect, and can literally make a child or unbelieving spouse, "holy".  In 1 Cor 7:14, we read, "For the unbelieving husband is consecrated through his (believing) wife, and the unbelieving wife is consecrated through her husband.  Otherwise, your children would be unclean, but as it is they are holy."  It is this faith of the parents, and Godparents, that asks for the gifts of Baptism on behalf of the child, which God graciously responds to.

St Paul also confirms that baptism now replaces circumcision as entry into the New Covenant.  For example, he says, "In Him you were also circumcised with a circumcision not administered by hand, by stripping off the carnal body, with the circumcision of Christ.  You were buried with him in baptism, in which you were also raised with Him" (Col 2:11-12).

In fact, an early council of the Church, the Council of Carthage [252 A.D.] met in part to consider exactly our question.  But the question wasn't whether to baptize babies or not.  No, the question was, that under the New Covenant, should we wait until the traditional eighth day of circumcision to baptize.  And the decision was to not even wait until the eighth day, but to baptize as soon as possible, without delay!

St. Peter further settles the issue for us.  As he gave the first great sermon of the Church on the day of Pentecost, converting some 3000 Jews at once, he would close, saying "Repent and be baptized, every one of you, ( i.e. babies too! ) in the name of Jesus Christ for the forgiveness of your sins; and you will receive the gift of the Holy Spirit.  For the promise is made to you and to your children" (Acts 2:38-39).

St. Peter makes it clear that children were included in this call to be baptized.  While having no need to repent of personal sin, babies certainly do need the great, freely given, unmerited gifts of baptism — the stain of original sin washed from their souls, the indwelling of the Trinity restored, Sanctifying Grace poured into their souls — making them children of God and members of the Body of Christ.

Additionally, in 1 Cor 1:16 and Acts 16:15,33, we see baptism of "whole households", with no mention of excluding babies. 

In Mark 10:14, Jesus Himself gives further confirmation of all this.  "People were bringing even infants (the Greek word here literally means infants, NOT older children) to Him that He might touch them....  'Let the children come to Me and do not prevent them; for the kingdom of God belongs to such as these..."  And He took them in His arms and blessed them, laying His hands upon them."  Awesome!

Now according to Scripture, Baptism is the normal way of entering into the Kingdom of Heaven.  "Amen, amen, I say to you, no one can enter the kingdom of God without being born of water and Spirit" (John 3:3-5).  "Being born of water and Spirit" is Baptism according to what the early Church taught about this passage.  If Jesus says the Kingdom of God belongs to infants and children, it would make no sense if He then withheld the gift of Baptism that would give them entrance to this very Kingdom.

Additionally, in 1 Cor 1:16 and Acts 16:15,33, we see baptism of "whole households", with no mention of excluding babies.  In fact, in all of Sacred Scripture, there is not a single place that says babies should not be baptized, not one.  Period!

But, what does the early Church have to say about this matter?  Lots!

Listen to St Irenaeus (A.D. 189), a disciple of St Polycarp who was taught by St John the Apostle himself!  "He [Jesus] came to save all through Himself; all, I say, who through Him are reborn in God: infants, and children... He passed through every age, becoming an infant for infants, sanctifying infants; a child for children, sanctifying those who are of that age".

The great St Augustine would write: "The custom of Mother Church in baptizing infants is...  not to be scorned, nor regarded as superfluous, nor is it to be believed that its tradition is anything except apostolic".

In his 215 A.D.  letter, "Apostolic Tradition", St Hippolytus would write: "Baptize first the children, and if they can speak for themselves let them do so.  Otherwise, let their parents or other relatives speak for them."

St Gregory of Nazianz summarizes the answer for us perfectly in his "Oration on Holy Baptism".  "Do you have an infant child?  Allow sin no opportunity; rather, let the infant be sanctified from childhood.  From his most tender age let him be consecrated by the Spirit."  Perfect!