2.5 year old singular sore

My son has this sore on his leg with no other noticeable symptoms, could it be ringworm or something else? Planning on taking him to the chemist when my car is back from its repairs later today. He has a rare chromosome disorder (large 20p duplication) so I’m always a bit more suspicious when it comes to his health. Photos in comments. Thank you

ETA: I think he’s had it for over a week. Definitely at least a week but just looked like smaller sore than this. Just noticed it wasn’t going away.