I Noticed Back In August That My 5 Year Old

I noticed back in August that my 5 year old had a black spot with slight bruising around it on the back of her thigh. I thought she may have pinched it somehow and it was just a blood blister. It seemed to have been healing for a few weeks. Yesterday while helping her dress, I noticed now, she has two black spots in the same area and it's still bruised. What could this possible be and should I be worried?