By the way, if he is not eating at all, liquid is essential. some pedialyte popscicles are good or even just regular popscicles. Little bits of water or watered down juice are good. But he needs to have some liquid intake. If he isnn't doing that, go immediately to your doctor. Small children can become dehydrated easily. good luck
Is this a sudden problem? Is he ill?
I have a child with sensory issues that carry over to food but refusal of all food and vomiting when given milk sounds more like a gi issue as stated or an illness. good luck
He may have a digestive problem. Has your pediatrician looked for food intolerance?.