Who Is Pinky I Have A 4 Year Old Son Who Continuously Gets These Cuts In The Bend Of His Pinky Toes.What Is This?

I have a 4 year old son who continuously gets these cuts in the bend of his pinky toes.What is this? - who is pinky

This happens only in the fifth finger, and it happens on both feet. The back foot on the floor of the same curve. He splits the whole time and bleeding. The cracks are large enough. She has healed after a few days, he seems out of action (was) with shoes, just crying and they're back.