I raised fawns for DNR rehab for years. Give this baby goat milk or goat milk replacer. Is it injured? They are very fragile. Use a goat milk. How old is it?? Very young fawns WILL NOT go to the bathroom unless you take a paper towel (is what I used) and rub it on their bottom. It simulates the doe licking. Don't give it cow milk. I raised as many buck fawns as doe fawns. I did not raise them to be pets and never had a problem with them. I did not socialize them with other animals outside of other fawns (baby goats for example), nor did I show them to a lot of people. You can pen it, but don't attempt to chain it out. They learn very fast to come when they are called for their bottle. I never grained them. One year I raised 8, but mostly 3. I never lost one that came to me healthy. Because of chronic wasting disease, the deer rehab program has been scratched in Mn and they are killed or left. Feed as much as you would a baby goat the same size. When I first had them and they were very young, I fed them 3 times a day, as much as 8 hours apart as I could. A doe only feeds the very young twice a day. After that they go with her and they snack ~ but that it neither pratical nor necessary for you though. You do not need an artificial heat source.
That is all I can think of for now.