Breasts size will not reduce by pressing ice cubes on them . The growth of the breasts depend on the hormonal
changes , breasts generally increase in size during puberty
and reach a good size after that. frequent handling of breasts, general weight gain, ocp's can all cause increase in size
But if your weight is less or hormonal disturbances, it will fail to grow, in some, familial causes , as in every women in family will have small breasts, such cases we cant do anything
Advise you to go for a check up to a Gynecologist and some hormone tests and could be treated accordingly, else padded bra, breast augmentation
surgeries are an option.