As he learns about the basic development of children, what are two things that the creature realizes are totally different about him in comparison to normal childhood?

The monster realizes that he had no parents..... no brothers or sisters. He also comes to understand that he has never seen a being that eben remotely resembled him.

"Other lessons were impressed upon me even more deeply. I heard of the difference of sexes; and the birth and growth of children; how the father doated on the smiles of the infant, and the lively sallies of the older child; how all the life and cares of the mother were wrapped up in the precious charge; how the mind of youth expanded and gained knowledge; of brother, sister, and all the various relationships which bind one human being to another in mutual bonds.

"But where were my friends and relations? No father had watched my infant days, no mother had blessed me with smiles and caresses; or if they had, all my past life was now a blot, a blind vacancy in which I distinguished nothing. From my earliest remembrance I had been as I then was in height and proportion. I had never yet seen a being resembling me, or who claimed any intercourse with me. What was I? The question again recurred, to be answered only with groans.