Anselm of Canterbury discusses his theology of original sin and the condemnation of infants before the reception of baptism.
Anselm of Canterbury, The Virgin Conception and Original Sin (De Conceptu Virginali et de Originali Peccato) 28–29, in Anselm of Canterbury: Complete Philosophical and Theological Treatises (trans. Jasper Hopkins and Herbert Richardson; N.P.: Ex Fontibus Co., 2016), 463–65
CHAPTER TWENTY-EIGHT
Against those who think that infants ought not to be condemned
There are those whose mind resists accepting [the view] that infants dying unbaptized ought to be condemned solely on account of the injustice of which I have spoken. There reasons are (2) that no man judges infants to be blameworthy as the result of another person’s sin, (2) that in such a state infants are not yet just and discerning, and (3) that God (so they think) ought not to judge innocent infants more severely than men judge them. These people must be told that God ought to act toward infants in one way and man [ought to act toward them] in another. For man ought not to demand from a nature what he has not bestowed and what is not owed to him. Nor does one man justly reproach another man for being born with a fault with which he himself is born and form which he himself is healed only by someone else. But God does rightly demand from a nature what He bestowed on it and what is rightly owed to Him.
But if we consider the matter, even this judgment by which infants are condemned is not much different from the judgment of men. For take the case of a man and his wife who not by their own merit but by favor alone (gratia sola) have been elevated to some great dignity and estate, and who together commit an unpardonably serious crime, and who on account of this crime are justly cast down and reduced to servitude. Who will say that the children whom they beget after their condemnation ought not to be subject to the same servitude but ought rather to be gratuitously restored to the goods which their parents rightfully lost? Such is the case with our first parents and with their descendants whom they—justly sentenced because of their own fault to [be cast down] form happiness into misery—beget into their own exile. Therefore, there ought to be like judgment for like cases; but in the case of our first parents the more reprehensible their crime can be shown to be, the more severely [it ought to be judged].
In last analysis, every man is either saved or condemned. But everyone who is saved is admitted to the Kingdom of Heaven; and everyone who is condemned is excluded therefrom. Now, assuredly, he who is admitted is elevated to the likeness of those angels in whom there never was and never will be any sin—something which cannot happen as long as there is any taint of sin in him. Thus, a man with any sin at all—even a small sin—cannot be saved. Hence, if what I have termed original sin is a sin, then it is necessary that every man who is born with it and does not have it forgiven is condemned.
CHAPTER TWENTY-NINE
How the inability to have justice excuses infants after their baptism.
I have said that the inability to have justice does not excuse the injustice of infants. Perhaps, then, someone will ask:
If there is sin, i.e., injustice, in an infant before his baptism, and if (as you say) the inability to have justice is no excuse, and if in baptism only sin which was prior thereto is remitted, then since after baptism an infant, for as long as he is an infant, lacks justice and cannot even understand the justice which he should keep (if indeed justice is uprightness-of-will kept for its own sake), why is he not also unjust after having been baptized? Thus, if a baptized infant dies in infancy (though not immediately after baptism) before he knows how to repent, then since he does not have the required justice, and since his inability does not excuse him, he passes from this life unjust (even as he would have done before his baptism), and he is not admitted into the Kingdom of God, into which no one who is unjust is received. But the Catholic Church does not hold to this view. Now, if in baptism a subsequent sin within infancy is remitted to infants, then why [are] not also those sins which are committed at a later stage of development [forgiven at the time of baptism]?
To this question I give the following answer. In baptism the sins which were present before baptism are completely blotted out. Accordingly, the original inability to have justice is not reckoned as sin in the case of those who have already been baptized—as [it is reckoned to them] prior [to their baptism]. Hence, just as prior to their baptism this inability could not excuse the absence of justice, since the inability was culpable, so after their baptism the inability completely excuses the absence of justice, because although the inability remains it is without any culpability. Thus it happens that the justice which before their baptism was required of infants, without any excuse on their part, is after their baptism not demanded of them as their requirement. Therefore, as long as it is only because of the original inability that they do not have justice, they are not unjust, since there is no absence in them of required justice. For what is both impossible and free of all culpability is not required. Therefore, if infants die in such a condition, then because they are not unjust they are not condemned; rather, by the justice of Christ, who gave Himself for them, and by the justice of faith on the part of the Church, their mother, which believes on their behalf, they are saved [being reckoned] as just.
In accordance with the capacity of my understanding I have briefly made these statements about original sin—not so much by way of asserting them as by way of provisionally inferring them—until God shall somehow reveal to me something better. But if someone has a different view, I do not reject anyone’s opinion provided it can be proved to be true.