Baby Blues
Rebbe Simlai (Niddah 30b) says that a fetus learns the entire Torah while in its mother’s womb. When the child is born, an angel hits the child on its mouth and it forgets everything.
Minhagim
Reasons for a Shalom Zachor in the Gemara
Why a shalom zachor is held on the first Friday night after a boy is born, and whether one is made for a girl or when the baby is absent.