16 These things, and others which I can advance, I am accustomed to state, as well as I can, against those who attempt to overthrow by such objections the opinion that souls are made for each individual, as the first man's soul was made for him.
But when we come to the penal sufferings of infants, I am embarrassed, believe me, by great difficulties, and am wholly at a loss to find an answer by which they are solved; and I speak here not only of those punishments in the life to come, which are involved in that perdition to which they must be drawn down if they depart from the body without the sacrament of Christian grace, but also of the sufferings which are to our sorrow endured by them before our eyes in this present life, and which are so various, that time rather than examples would fail me if I were to attempt to enumerate them. They are liable to wasting disease, to racking pain, to the agonies of thirst and hunger, to feebleness of limbs, to privation of bodily senses, and to vexing assaults of unclean spirits. Surely it is incumbent on us to show how it is compatible with justice that infants suffer all these things without any evil of their own as the procuring cause. For it would be impious to say, either that these things take place without God's knowledge, or that He cannot resist those who cause them, or that He unrighteously does these things, or permits them to be done. We are warranted in saying that irrational animals are given by God to serve creatures possessing a higher nature, even though they be wicked, as we see most plainly in the gospel that the swine of the Gadarenes were given to the legion of devils at their request; but could we ever be warranted in saying this of men? Certainly not. Man is, indeed, an animal, but an animal endowed with reason, though mortal. In his members dwells a reasonable soul, which in these severe afflictions is enduring a penalty. Now God is good, God is just, God is omnipotent— none but a madman would doubt that he is so; let the great sufferings, therefore, which infant children experience be accounted for by some reason compatible with justice. When older people suffer such trials, we are accustomed, certainly, to say, either that their worth is being proved, as in Job's case, or that their wickedness is being punished, as in Herod's; and from some examples, which it has pleased God to make perfectly clear, men are enabled to conjecture the nature of others which are more obscure; but this is in regard to persons of mature age. Tell me, therefore, what we must answer in regard to infant children; is it true that, although they suffer so great punishments, there are no sins in them deserving to be punished? For, of course, there is not in them at that age any righteousness requiring to be put to the proof.
17. What shall I say, moreover, as to the [difficulty which besets the theory of the creation of each soul separately at the birth of the individual in connection with the] diversity of talent in different souls, and especially the absolute privation of reason in some? This is, indeed, not apparent in the first stages of infancy, but being developed continuously from the beginning of life, it becomes manifest in children, of whom some are so slow and defective in memory that they cannot learn even the letters of the alphabet, and some (commonly called idiots) so imbecile that they differ very little from the beasts of the field. Perhaps I am told, in answer to this, that the bodies are the cause of these imperfections. But surely the opinion which we wish to see vindicated from objection does not require us to affirm that the soul chose for itself the body which so impairs it, and, being deceived in the choice, committed a blunder; or that the soul, when it was compelled, as a necessary consequence of being born, to enter into some body, was hindered from finding another by crowds of souls occupying the other bodies before it came, so that, like a man who takes whatever seat may remain vacant for him in a theatre, the soul was guided in taking possession of the imperfect body not by its choice, but by its circumstances. We, of course, cannot say and ought not to believe such things. Tell us, therefore, what we ought to believe and to say in order to vindicate from this difficulty the theory that for each individual body a new soul is specially created.
Source: Letters (New Advent)