Objection 1. It would seem that in the state of innocence children would have been born confirmed in righteousness. For Gregory says (Moral. iv) on the words of Job 3:13: "For now I should have been asleep, etc.: If no sinful corruption had infected our first parent, he would not have begotten "children of hell"; no children would have been born of him but such as were destined to be saved by the Redeemer." Therefore all would have been born confirmed in righteousness.
Objection 2. Further, Anselm says (Cur Deus Homo i, 18): "If our first parents had lived so as not to yield to temptation, they would have been confirmed in grace, so that with their offspring they would have been unable to sin any more." Therefore the children would have been born confirmed in righteousness.
Objection 3. Further, good is stronger than evil. But by the sin of the first man there resulted, in those born of him, the necessity of sin. Therefore, if the first man had persevered in righteousness, his descendants would have derived from him the necessity of preserving righteousness.
Objection 4. Further, the angels who remained faithful to God, while the others sinned, were at once confirmed in grace, so as to be unable henceforth to sin. In like manner, therefore, man would have been confirmed in grace if he had persevered. But he would have begotten children like himself. Therefore they also would have been born confirmed in righteousness.
On the contrary, Augustine says (De Civ. Dei xiv, 10): "Happy would have been the whole human race if neither they--that is our first parents--had committed any evil to be transmitted to their descendants, nor any of their race had committed any sin for which they would have been condemned." From which words we gather that even if our first parents had not sinned, any of their descendants might have done evil; and therefore they would not have been born confirmed in righteousness.
I answer that, It does not seem possible that in the state of innocence children would have been born confirmed in righteousness. For it is clear that at their birth they would not have had greater perfection than their parents at the time of begetting. Now the parents, as long as they begot children, would not have been confirmed in righteousness. For the rational creature is confirmed in righteousness through the beatitude given by the clear vision of God; and when once it has seen God, it cannot but cleave to Him Who is the essence of goodness, wherefrom no one can turn away, since nothing is desired or loved but under the aspect of good. I say this according to the general law; for it may be otherwise in the case of special privilege, such as we believe was granted to the Virgin Mother of God. And as soon as Adam had attained to that happy state of seeing God in His Essence, he would have become spiritual in soul and body; and his animal life would have ceased, wherein alone there is generation. Hence it is clear that children would not have been born confirmed in righteousness.
Reply to Objection 1. If Adam had not sinned, he would not have begotten "children of hell" in the sense that they would contract from him sin which is the cause of hell: yet by sinning of their own free-will they could have become "children of hell." If, however, they did not become "children of hell" by falling into sin, this would not have been owing to their being confirmed in righteousness, but to Divine Providence preserving them free from sin.
Reply to Objection 2. Anselm does not say this by way of assertion, but only as an opinion, which is clear from his mode of expression as follows: "It seems that if they had lived, etc."
Reply to Objection 3. This argument is not conclusive, though Anselm seems to have been influenced by it, as appears from his words above quoted. For the necessity of sin incurred by the descendants would not have been such that they could not return to righteousness, which is the case only with the damned. Wherefore neither would the parents have transmitted to their descendants the necessity of not sinning, which is only in the blessed.
Reply to Objection 4. There is no comparison between man and the angels; for man's free-will is changeable, both before and after choice; whereas the angel's is not changeable, as we have said above in treating of the angels (64, 2).
Source: Summa Theologica (New Advent)