Girls at the age of 8 years old may have breast development. Currently, due to disease factors or dietary factors, the estrogen level in girls’ bodies may rise, which may lead to precocious puberty or early sexual development. If a girl develops breasts before the age of 8, the clinical diagnosis is precocious puberty, and if breast development occurs before the age of 11, the diagnosis is early sexual development. If a girl reports pain in the breast area or feels uncomfortable after growing a nucleus, parents should actively take the child to the hospital for ultrasound examination to clarify whether it is breast growth or premature development. In the case of early sexual development or precocious puberty in girls, ultrasound and bone age tests should be performed to clarify the extent of development and whether treatment is needed, depending on the actual situation.