During puberty, girls begin producing extra estrogen in the ovaries and boys begin producing extra testosterone in the testicles. These hormones produce the physical and emotional changes associated with puberty, such as breast development in girls and enlarged testicles and penis in boys.
When certain hormones are released too soon, a child can enter puberty earlier than he or she should. This may be the result of a condition called central precocious puberty (CPP). There is no direct cause for CPP in most cases, but in rare cases it may be due to an underlying medical condition.