Gutmutter - I don't post much, but I am a regular reader here at FORT and saw your post.
Let me start by saying that I'm very sorry for the worry you are feeling right now.
There are many other things besides "the worst" that the lump could be. Your doctor asked if you had taken a blow to the area because if there had been some kind of trauma to the area (a fall, or getting hit with something for example), it could cause a hematoma (a pocket of blood under the skin), that could feel like a lump. There are also Fibrocystic breasts (connective tissue scars), Fibroadenomas (glandular and connective tissue), Papillomas (growths), or Fat necrosis (fatty tissue). As well as a bunch of other benign (non-cancerous) explainations. The biopsy is done to determine what it is by what kind of cells or tissue is collected. No one knows all the facts until the biopsy is done but, keep in mind that today's data is that about 80% of breast lumps are non-cancerous.
My best advice to you is to research and inform yourself before you go in for the biopsy so that when you do get your results you have a better understanding of what it all means. There are a bunch of web sites that focus on women's health issues. Here is a good one that has a section on breast health and has alot of information:
As far as telling the kids , Im sure that they do feel your anxiety, but until you know the whole story I wouldnt tell them a whole lot. Maybe just that your having a health issue and having tests done, and that you will discuss it further when you know more. (I don't know your kids or how they deal with stress so it's hard for me to know how best to approach them). I think you will know when it's right and what to say when the time comes.
I really hope that this helps you and maybe even ease your mind a little bit.
Take care of yourself and please let me know how things go (you can pm me if you like). I will keep you in my prayers...