Benign premature thelarche is a noncancerous condition that causes early breast development in female toddlers and young girls.  Slightly elevated levels of hormones in female children can result in the growth of breast tissue in one or both breasts for several months. Then the extra breast tissue either:
• Disappears spontaneously
• Stays at the size of a very small breast until it begins to develop into a breast of a normal size at the time of puberty
If you notice that the breast or breasts of your young daughter or young grand-daughter's is/are developing prematurely, contact a pediatrician for a proper diagnosis. Rapid growth of a breast or breasts in a young female child may be due to a serious hormonal condition.  Therefore, it is important for a doctor to determine whether premature breast development is due to benign premature thelarche or a serious hormonal condition.
1. C. McCarthy. Babies with breasts. Parenting. 07/06; 39.