That kitten needs to see a vet. His skin should not be like that. It's all around his mouth too. It looks like some sort of rash - maybe thrush.
He will need medication to cure it, and it's probay contagious too, so please get him to the vet asap!
He will need medication to cure it, and it's probay contagious too, so please get him to the vet asap!