This is usually called premature thelarche, all babies go through what we call minipuberty near birth and in girls there is a surge of some hormones from the brain
that then
go away and some can develop a little response
that shows as breast buds, these usually resolve due to lack of ongoing pubertal levels of hormones and by age 3 this should be gone, however if this is enlarged compared to prior exam then workup may be needed, firstly to measure the brain hormones that stimulate the ovaries to