The development of the uterus in children generally occurs between the ages of 12 and 14. The development of secondary sexual characteristics occurs between the ages of 9 and 11. The first to develop are the breasts, followed by the appearance of pubic hair, axillary hair, enlargement of the labia majora and minora, hyperpigmentation, and the appearance of white vaginal discharge. The onset of menstruation two and a half to three years after the baby’s breast development, usually at the age of 12-14, marks the maturity of female reproductive function, when the uterine ovaries increase in size and mature ovulation can occur. If a baby develops breasts before the age of eight, it may be precocious and should be seen promptly. In addition, if a girl still does not have secondary sexual characteristics after the age of 14, she has delayed sexual development and should pay attention to the effects of diseases, so she also needs to see an endocrinologist in time.