It is difficult to decide from your description whether your son has thrush or if he has actual sores in his mouth . If you think that he has sores then he has a condition called herpes stomatitis.The sores in the mouth are painful and children with herpes stomatitis do not want to eat or drink. You can try applying Teejel gel to the sores in your son's mouth but if he still will not eat or drink he should be taken to a paediatric clinic in case he becomes dehydrated and needs admission to hospital for fluids.
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