When onset of puberty occurs prematurely (before the ages of 7 - 9) it is known as precocious puberty.
Signs of this condition include things like premature breast development and onset menstruation in girls. Boys may see premature enlargement of the testicles or penis as well as early onset of pubic hair.
A pediatric endocrinologist is best suited to diagnose and recommend treatment for precocious puberty.
In the case that precocious puberty comes as a result of an underlying disease, like a tumor, your physician will treat that specific problem to halt the premature development.
When the condition is not resulting from another health problem, hormonal treatment may be recommended. Synthetically produced drugs can often block production of the sex hormones that cause premature puberty and reverse its signs.