Growhts On Bones

My little girl has growths on the bones in her legs. They are on her knee and ankle joints. She sometimes have pains. She has been to a bone specialist and she said it was swellings and they don't normally treat them in children. She is only six years old. Please tell me what this is and how it can be treated. I have also been told that these growths can stunt a childs growth. What can I do? The swellings are getting worse, but her doctor acts as if it's no big deal.