According to the usage of the Church, Baptism is given even to infants.
And indeed if there were nothing in infants which required a remission of
sins and nothing in them pertinent to forgiveness, the grace of Baptism
would seem superfluous.
Origen, Commentaries on Romans 5, 9 (inter 244-254 AD)
The Church received from the Apostles the tradition of giving Baptism
even to infants. For the Apostles, to whom were committed the secrets of
divine mysteries, knew that there is in everyone the innate stains of sin,
which must be washed away through water and the Spirit.
St. Cyprian of Carthage, Letters to Fidus 64 (59), 5 (c. 251-252 AD)
As to what pertains to the case of infants: you said that they ought not to
be baptized within the second or third day after their birth...and that you did
not think that one should be baptized and sanctified within the eighth day
after his birth. In our council it seemed to us far otherwise.
St. Gregory Nazianzus, Oration on Holy Baptism 40, 17 (381 AD)
Do you have an infant child? Allow sin no opportunity; rather, let the
infant be sanctified from childhood. From the most tender age let him be
consecrated by the Spirit. Do you fear the seal because of the weakness of
nature? O what a pusillanimous mother, and of how little faith!
Give
your child the Trinity, that great and noble protector.
St. Augustine of Hippo, The Interpretation of Genesis 10, 23, 39
(inter 401-415)
The custom of Mother Church in baptizing infants is certainly not to be
scorned, nor is it to be regarded in any way as superfluous, nor is it to be
believed that its tradition is anything except Apostolic. The age of infancy