I hope you people never eat the complimentary peanuts on the bar counter.
And I hope you never toucoh the handrail on an escalator. It is STDs all over it.
lol
You obviously never see them cleaning that stuff before? AFAIK its done daily.
The problem with both of those scenarios is people don't wash their hands after going to the bathroom.
But contracting an STD from touching an escalator handrail? Unless you immediately go touch yourself sexually after doing so I doubt it.
As for the peanuts, I never eat **** like that when it's available to a bunch of drunk people

Even finger foods (when served at a public place) I make sure has utensils to pick them up, otherwise I'd use my fingers, however, I'd have the common courtesy not to put anything back I took but didn't eat. That's just weird... plus usually those are served at parties where you're more likely to encounter people you already know so why not.
Watch the YouTube video please, some cursing in there, but I think you guys would get the idea
Back to the OP: I doubt they're swopping spit with the baby by kissing them on the lips unless both parties slobber all over each other and push their tongue in the babies mouth. Then you have a different thing to worry about.
Having said that. I love using this phrase, it's in Afrikaans so I hope you understand it.
Muis... pis uit die peper uit...
Because pepper really burns if you rub it on your private parts (don't ask me how I know that) and you have no business telling the parents what to do or what not to do. If they feel they want to kiss their child on the lips then let them. The only way anyone really learns (and takes advices) is in hindsight, and hindsight is 20/20. All you can then do is "I told you so" which they'll love at that point when their child, without teeth, has gum disease according to you.
Not that anyone doesn't brush their teeth daily (twice/three times a day) like you're suppose to... oh wait? They do?
Technically speaking gum disease through kissing is possible if you're filthy... and kiss another filthy person... that has gum disease... and then just don't brush your teeth at all for a period.... so that it'll sink in...
Germs.... people tend to be more scared of them than the hijacker about to blow their brains out .... but heh... go ahead... live your life like that. You only have 1 so why the hell spoil all the fun with *maybe* getting sick if you don't watch what you touch or eat or do.... because of germs.