With young girls beginning their menstrual cycles as young as 9 years of age today, it's not unusual for their breasts (known as "breast buds") to start to develop and mature soon after. Girls will often notice some early signs of this, including an aching in their chest, soreness from sleeping on their chest at night, and a tingling sensation that feels unusual and new. These are all signs that puberty has arrived and their breasts are developing.
Girls' breasts develop at different rates, which can be frustrating for a young girl who feels the need to compare her breast development progress to that of other girls in her school class. Tell her that all good things come in time. It's also not unusual for one breast to grow at a different rate than the other - also frustrating, and even alarming, for her. You can reassure her that her breasts will eventually even out.
Breasts take several years to mature and grow to full size. As the breasts develop, tiny glands on the areola will commonly produce a whitish fluid. This is normal and is triggered by hormonal changes. During this time, a girl may also experience a periodic milky discharge from the nipple, again related to hormonal changes.
Lumps and bumps may also come and go because of the same shifting hormone levels. Girls are curious about their growing breasts, however, and may confuse these little bumps with pimples and attempt to squeeze them dry. Explain to them that this isn't acne and so there's no need to squeeze. Of course, if they've already squeezed the bumps, reassure them that no harm has been done but that they shouldn't keep squeezing the lumps because they could get infected.
Sometimes a lump may appear that doesn't go away and becomes increasingly more firm; most likely this is a benign growth known as a fibroadenoma. These benign masses are more common among women younger than 45 and can develop even in teenage breasts. If such a lump appears, your daughter's doctor may recommend an ultrasound to confirm this diagnosis.
As soon as your teen's or tween's breasts begin to take shape, get her fitted for a bra. She doesn't need other students giggling at her in school because they can see her nipples projecting through her clothes. She may want to take a girlfriend with her, especially someone who has already been fitted. (It's a girl thing, so just go along.)
Whether you are ready or not, this is also the time to talk more seriously about sexual activity and your thoughts, feelings, and moral beliefs regarding sexuality. Don't be tempted to scare your daughter with misinformation (i.e., that heavy petting in the backseat of a car will cause her to get breast cancer) but, if you're like me, you can tell her that such behavior would cause her father to ground her for a year.