It is normal for a little girl’s breasts to begin to develop at the age of 10, indicating the development of secondary sexual characteristics, which can also be manifested in the appearance of pubic hair and armpit hair, and the onset of menstruation. Under normal circumstances, the age of the girl’s breast development in the age of 9 ~ 11 years old, so, the little girl 10 years old breasts began to develop is normal, do not worry too much. Breast development is a manifestation of the development of secondary sexual characteristics, indicating that it has entered puberty, which is a physiological phenomenon. When the breasts begin to develop, there will be localized pain, mild bulging, areola enlargement and other manifestations. In addition, the development of secondary sexual characteristics of girls can also be manifested in the emergence of pubic hair, armpit hair, as well as the onset of menstruation. For women, the development of secondary sexual characteristics is mainly related to the function of the hypothalamic-pituitary-gonadal axis. To summarize, when a girl’s breasts develop, parents need to teach their children to take proper care of their breasts, keep their moods happy, and strengthen the intake of nutrients. If there are any other discomforts, they should consult a doctor in time.