Look like veruccas. Apple cider vinegar on cotton wool taped on foot overnight. After a couple of nights can file or scrape away "dead" top layer. Repeat. Will take a few weeks but effective in a way that about £100 of various treatments from chemists over a couple of years never was for me. Doesn't seem to make skin sore like commercial treatments (but probably worth doing a test for a couple of hours rather than overnight if a young child). Also worked for a family member with a collection of veruccas looking much worse than the picture. Good luck!