My 5 year old nieces can. We were walking down the street and someone came walking with their GSD, and one of them said, "Look, a German Shepherd Dog." He smiled and said, "they know their dog breeds."
Well, really, they do not know all of them. One of their aunties who is a who has GSDs takes them to her house and lets them play with puppies though, and then takes them to Grandma and Grampa's house so they can see Cujo. And she gives them Puppy issues of Dogs USA that they immediately start reading and trying to figure out what the different breeds are. And she takes them to dog shows and gets their pictures taken with an English Setter, and shows them Obedience, and Rally, and different breeds. But I have to admit, that they can readily identify a German Shepherd Dog, so in my opinion, their dog-breed-identification knowledge is good enough. They can start work at petsmart.
Oh and if the puppies start biting their hands, they know to close their fist so the puppy will be less likely to want to bite their hands. It actually works, and lots of adults don't know that. They know to ask politely to pet a dog, and they understand that sometimes people will say no. They know how to approach a dog, and they know not to approach a dog they do not know. Their auntie has been given the task of teaching them about dogs. Though their mother will take them to pet stores to let them pet the puppies.