One a baby has had hfmd is he immune to it or can they get it again?

a lot of babies get immune to the virus that caused hfmd once they have it for the first time. But because the disease can be caused due to various factors, it is possible that a baby can get it again. it is a very contagious disease that easily spreads through secretions from the nose, mouth, through the fluid in blisters and also through feces. as a result, it can affect a baby again, even if baby has already suffered from it earlier. i would suggest you read up a bit more about it here https://www.cdc.gov/features/handfootmouthdisease/index.html