My daughters breast is sore and has a small hard lump she's only 8 . what could this be? should i worry?

Probably not: Sounds like an benign breast bud many children experience before puberty. If you are concerned, then a visit to her doctor will help further define it and let you know what to expect.

Normal tissue: Thelarche is the term used for the emergence of breast tissue in the beginning stages of puberty. A spongy bit of true breast tissue is located directly under the nipple on one or both sides. It can be tender to touch & one side may emerge weeks before the other.Your pcp can confirm this process, i HAV at least 3-5 /yr come to my office for the same question.