The puppies are at that age where they are being mouthy. (and puppy teeth are sharp) All dogs need to be taught to NOT put their mouths on a humans skin.
This is information from a puppy class I took:
MOUTHING
*Puppies mouth each other in the litter and now that you are their new pack, they will probably mouth on you.
*Whenever your puppy starts to mouth on you, say AHH, AHH or similar word and put a toy in their mouth.
*Place a toy where in the areas of the home the puppy stays so that you can give it the them as soon as they start to mouth on you. ( I sometimes use a bully stick too)
*Try ignoring your puppy. When you puppy starts to mouth you or play too rough, simply stand up, cross your arms and turn away from your puppy.
NIPPING
*very common in puppies
*when your puppy puts his teeth on you, let out a LOUD yelp
I highly recommend getting your puppies enrolled in a PUPPY KINDERGARTEN class very soon. You will learn so much. Your puppy will learn from you. Honestly, I learned more in Puppy Kindergarten than in Basic Obedience. If I did it over again, I don't think I would have even done the Basic Obedience since 80% of the information was in Puppy Kindergarten and the other information I don't really use anyway.