AapThe AAP says (American Academy of Pediatrics):
Foreskin retraction occurs when the foreskin can be pulled back away from the glans toward the abdomen. This process happens on its own. When it happens is different for every child. It may take a few days, weeks, months, or even years. [Or the foreskin may never become retractable.] This is normal. Most boys will be able to retract their foreskins by the time they are 18 years old. Some foreskins retract soon after birth. Separation can even occur before birth, but it is rare. As a boy becomes more aware of his body, he will most likely discover how to retract his own foreskin. Sometimes the foreskin will puff out, like a balloon, while a boy urinates. This is normal and is a sign that the foreskin and the glans have begun to separate from each other.
[Bravo! The normality of ballooning is seldom admitted. Ballooning is commoner in small boys than young men.]
Foreskin retraction should never be forced. While the foreskin is still attached to the glans of the penis, do not try to pull it back, especially in an infant. Forcing the foreskin to retract before it is ready may harm the penis and cause pain, bleeding, and tears in the skin.