Maybe scars? My daughter itches her mosquito bites and they leave round scars like that. I use Moderna cream and they eventually go away.
Check with Dr. if these are constant bruises could maybe have to do with low iron? Just a thought not a Dr but maybe something to discuss. Good luck
Toddlers get bruises near the shin area all the time. It should heal with in a few weeks. But if she is bumping into the same thing daily then thats probably why it doesn’t seem to heal. Maybe see what she might be continuously bumping into. A toy box, her chair before sitting, climbing up on to something (bed frame, tall chair). It never hurts to get seen by her pediatrician.