Any licking of the face is unhygienic and even dangerous, especially if it is a face of a baby.
Puppies carry the eggs from a worm infestation on their tongues and mouths from licking themselves, and these could be transmitted to youe baby, causing a serious complaint of the muscles, which could, years later, cripple the child. Always be sure to have your puppy thoroughly wormed before admitting it to the family circle.
Also, be sure to wash your puppy's face and mouth at least once a day. Remember, they eat their food with much splashing and they are not like cats, who clean themselves with their paws; they can't clean more than can be reached by the tongue.
Provided your puppy is wormed and washed, an occasional lick for the baby will do no harm at all. Whatever happens, don't let your baby pick up your anxiety. There is nothing so pathetic as a child who is afraid of puppies.