Hi my 4 year old got chicken pox and was told not to worry about the 8 months old son, he would not get it as I was breast feeding him, he was under a year old and if he did it would be a few spot. Well he did get it and he was covered from head to toe, In his mouth, between toes and fingers everywhere. it was the worse case that most of if not all my friends and family had seen in any age.
Keep him cool and he should wear light weight clothes nothing to tight. I gave my son Piriton medicine for the itching and gently put on Aqueous-Calamine cream. I also put a few drops of tea tree in a cup of milk and put it in a warm-ish bath. Do Not put the Tea tree neat in the bath, it must be mixed with a little milk as it will lie on the top of the water like oil and will burn his skin when you put him in. This will help with the healing of the spots.
Keep his nails short so if he tries to scratch he can only do a little damage to his skin, or put long socks on his hands so he can not pull or rub them off.
You have to look long and hard at my son who is now almost two to see any scars and he had a few nasty scars on his face by his eye. They have gone. He only has a few pit marks on his body. if he does get them and scars then he is young enough for them to fade away or go altogether.
He may not want to eat much, or he may want to nurse more.
Hope this helps and good luck.