Red mark on DS foot for around 2 weeks

[Amall221]

I have noticed a mark on DS foot, and at the beginning thought nothing of it. He is 22m so is always falling, however 2 weeks on and the mark is still there. It looks harmless but was just wondering if anyone had experienced something similar and could advise on what it could be.

Wouldn't be a part of his shoe rubbing it?

Initially I thought the same but its been there for some time now, even when he hasnt worn shoes for a long period of time