Actually, daycare and preschool should be teaching them to keep their hands, lips and other body parts to themselves.
Just "No kissing, Sweetheart. No one wants to spread germs around.".
They learn to sneeze into their elbow and wash hands a lot too.
Additional:
Why shouldn't it be about germs?
Between Hand, Foot, Mouth, flu, RSV, and any number of other things they can catch (yeah I know a lot of that can be airborne) does any kid really NEED direct mouth to mouth contact with anyone who may or may not be vaccinated against the typical childhood diseases (measles, mumps, rubella, chicken pox, etc)?
Sure they get exposed to plenty, but teaching to keep their mouths off other people will serve them well.