Hand foot and mouth

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So I’m pretty sure my 2.5yr old has hand foot and mouth. She had a fever of 101° on Saturday and then today I noticed a red bumpy rash under her bottom lip and looked inside her mouth and she has red dots on the top of her mouth and some at the back of the throat.

My question is I still breastfeed her here and there and also breastfeed my 3month old. How do I keep the 3month old from getting it from the breast?