When my dogs would act that way I would bite them back (especially the ears which are more sensitive areas). A dog trainer told me that puppies go trough a stage where they dont know their strenght and learn with each other the limit. It is not always about the teeth growing; puppies like to bite and play that way.
If you bite the dog right after he bites you just enough to make him squeal a bit he should understand. I would always hold my dog down too in submission position as I'd do it. I know this is strange but hey, worked for me
