My 2 yr old sucks his thumb, so much it's callased. (sp?) I think about the germs he must be putting in his mouth non-stop. All I can do right now is teach him about washing his hands which he loves to do now. I know you can't really do that with your 6 mo old, but they are going to run into one thing after another when it comes to bad habits and germs. Positive reinforcement is about the best thing you can do and try to teach them early. Kids will be kids...cf or not!!