This article gives sound advice http://www.thedogtrainingsecret.com/blog/give-kiss-understanding-dog-language/ including:
Keep your kids out of the face of other dogs!
Don’t ever let them hug or kiss a dog they don’t know, and be cautious about allowing them to get in the habit of doing it to your family pet.
Your dog may not mind; but their best friend’s dog may! So preventing the bad habit from forming is sometimes key!