Can someone tell me something, this might sound very stupid but I'm uneducated about this...

My MIL and also a good friend of mine gets cold sores .....

Is it very contagious???? They always kiss my baby and I really really don't want him to get the virus !!!

Can you catch it if they don't have an active cold sore and how can I tell them nicely that I don't want them kissing my baby..... ???

Thanks so much