It’s common for girls to feel small lumps on their chest as their breasts are developing. Some girls will also complain of “tingling or aching” (in the chest area) as the breasts are growing. One side will often develop before the other but the second side usually catches up in about 3-6 months. The lump that your daughter found is likely a “breast bud“, however we recommend making an appointment with your her primary care provider to be sure. It could be a sign of infection, but this is rare.