Girls between the ages of 8 and 13 and boys between the age of 10 and 15 undergo many physical and emotional changes as they grow up from being a child to eventually becoming an adult. This period of adolescence, with all the changes that happen during this time, is referred to as puberty.

A few examples of such changes noticeable in girls are development of breasts, appearance of pubic hair and the beginning of menstruation. With respect to boys, appearance of facial and pubic hair, deepening of voice and development of muscles are examples of such changes.

It is important to remember that the time of onset of puberty and its completion varies at an individual basis.

illustration of puberty, an adolescent girl in front of the mirror worried about acne on her face while an adolescent boy looking at a mirror admires a little bulge in his biceps, girl and boy exchanging side glances - Menstrupedia
References:
  1. Time to Change, http://kidshealth.org/
  2. When Is Puberty Too Early? http://www.dukehealth.org/