Whats this

It's hard to say for certain without seeing a clearer image or knowing more about the symptoms, so it's difficult to give you a proper answer here. There are quite a few skin conditions that can look similar to each other, and some need specific treatment while others might resolve on their own. The safest thing would be to bring your child to see a PD or polyclinic doctor, since they can examine it properly and give you the right diagnosis and treatment. Trying to treat it based on guesses online can sometimes make things worse, so a proper consult is really the way to go here.