Augustine of Hippo, On the Merits and Forgiveness of Sins, and on the Baptism of Infants I.25: Infants are Described as Believers and as Penitents. Sins Alone Separate Between God and Men

Chapter 25.—Infants are Described as Believers and as Penitents. Sins Alone Separate Between God and Men.

Some one will say: How then are mere infants called to repentance? How can such as they repent of anything? The answer to this is: If they must not be called penitents because they have not the sense of repenting, neither must they be called believers, because they likewise have not the sense of believing. But if they are rightly called believers, because they in a certain sense profess faith by the words of their parents, why are they not also held to be before that penitents when they are shown to renounce the devil and this world by the profession again of the same parents? The whole of this is done in hope, in the strength of the sacrament and of the divine grace which the Lord has bestowed upon the Church. But yet who knows not that the baptized infant fails to be benefited from what he received as a little child, if on coming to years of reason he fails to believe and to abstain from unlawful desires? If, however, the infant departs from the present life after he has received baptism, the guilt in which he was involved by original sin being done away, he shall be made perfect in that light of truth, which, remaining unchangeable for evermore, illumines the justified in the presence of their Creator. For sins alone separate between men and God; and these are done away by Christ’s grace, through whom, as Mediator, we are reconciled, when He justifies the ungodly.