Cold sore question!!

R

So we took our 5 month old over to see some family today and this was their first time meeting her, we forgot to give the whole “no kisses” speech and one of them kissed baby a few times, I noticed and mentioned it and they were more than understanding but then an hour or so later they mentioned they have a cold sore in their mouth 🙃 I about lost my mind and now I’m worrying like crazy. Does anyone know what can happen or what I should be looking out for? I don’t want anything to happen to my peanut and I’m anxious as is and kind of freaking out now.