Objection 1. It would seem that in the state of innocence children would have been born with perfect knowledge. For Adam would have begotten children like himself. But Adam was gifted with perfect knowledge (94, 3). Therefore children would have been born of him with perfect knowledge.
Objection 2. Further, ignorance is a result of sin, as Bede says (Cf. I-II, 85, 3). But ignorance is privation of knowledge. Therefore before sin children would have had perfect knowledge as soon as they were born.
Objection 3. Further, children would have been gifted with righteousness from birth. But knowledge is required for righteousness, since it directs our actions. Therefore they would also have been gifted with knowledge.
On the contrary, The human soul is naturally "like a blank tablet on which nothing is written," as the Philosopher says (De Anima iii, 4). But the nature of the soul is the same now as it would have been in the state of innocence. Therefore the souls of children would have been without knowledge at birth.
I answer that, As above stated (99, 1), as regards belief in matters which are above nature, we rely on authority alone; and so, when authority is wanting, we must be guided by the ordinary course of nature. Now it is natural for man to acquire knowledge through the senses, as above explained (55, 2; 84, 6); and for this reason is the soul united to the body, that it needs it for its proper operation; and this would not be so if the soul were endowed at birth with knowledge not acquired through the sensitive powers. We must conclude then, that, in the state of innocence, children would not have been born with perfect knowledge; but in course of time they would have acquired knowledge without difficulty by discovery or learning.
Reply to Objection 1. The perfection of knowledge was an individual accident of our first parent, so far as he was established as the father and instructor of the whole human race. Therefore he begot children like himself, not in that respect, but only in those accidents which were natural or conferred gratuitously on the whole nature.
Reply to Objection 2. Ignorance is privation of knowledge due at some particular time; and this would not have been in children from their birth, for they would have possessed the knowledge due to them at that time. Hence, no ignorance would have been in them, but only nescience in regard to certain matters. Such nescience was even in the holy angels, according to Dionysius (Coel. Hier. vii).
Reply to Objection 3. Children would have had sufficient knowledge to direct them to deeds of righteousness, in which men are guided by universal principles of right; and this knowledge of theirs would have been much more complete than what we have now by nature, as likewise their knowledge of other universal principles.
Source: Summa Theologica (New Advent)