Objective To investigate the risk factors associated with breast development in infants and young children, and to raise awareness of the disease. Methods 207 cases of infant girls with premature thelarche, 87 cases of healthy infant girls without secondary sexual characteristics were measured in serum estradiol, follicle stimulating hormone, luteinizing hormone levels, then filled out the survey questionnaire. Results Family near polluting factories, the mother early age at menarche, high frequency use of plastic products ( bottles, tableware, toys, food packaging materials, et al.), the mother during pregnancy often online, often eat animal food or high-protein diet, often eat fried food, drinks, puffed food sucker pigmented foods containing preservatives, feeding patterns (formula feeding, mixed feeding), estradiol value were closely related to 0 to 2-year-old girl's breast early development. Conclusion Environmental pollution around the family, the mother early menarche, bad eating habits, regular internet users during the mother's pregnancy, feeding with formula feeding or mixed feeding mainly elevated serum estradiol are closely related to 0 to 2 year-old girl's premature thelarche.