This is advice from a professional friend of mine:
Biting is a normal puppy behaviour. Puppies investigate the world through their mouths. If it is within reach, it will probably be picked up and chewed! If it is exciting and moves fast it will definitely get bitten. Dogs play by using their mouths because they dont have hands.
Puppies need to bite and they need to play. What she is doing is simply trying to elicit play. Play is by far the best way to bond with your pup and is a great way to reward her during training.
Use tug toys that she can bite. Old knotted towels or a favourite toy with string attached. Unwanted dressing gown cords are ideal. You need to encourage her to bite one end of the toy whilst you hold the other end. Then you can have a great game together without getting bitten.
Ensure your tug toys are long enough and soft enough for your puppy to happily bite. Your toy should touch the floor whilst you are holding the other end. This allows you to animate the toy and keep the game low to the ground and not encourage jumping up. It also puts distance between teeth and hands.
Keep these interactive toys out of your pups reach whilst they are not being played with. It will keep them more novel which means the pup is more likely to want to bite and play with them when given the opportunity. Plant toys around the house and garden (out of puppies reach) so you have them easily accessible and as much as possible, take the game outside.
Rotate chew items that you leave on the floor to also keep them interesting.
Do not play with your puppy unless you have a toy for her to grab. Don't let anyone in the house roughhouse with her or roll about on the floor with her.
Oh and to clarify he will have been mouthing his puppy siblings which is the important stage for him so you are right, it is an important stage with other pups but must not be allowed with humans from day one. He will have done the learning he needs to do by the time he gets to you.
Puppy mouthing is totally normal and yes, is part of learning bit inhibition and having a soft mouth. However once you have pup home it's important to not ignore it. If pup mouths your or one of your children, remove your hand and offer a toy. Reward for mouthing the toy. Repeat.
If there's no toy near by and the puppy mouths whilst getting attention stand up and leave, game over, the second he does it. He learns that mouthing = no fun.
Finally if he is prolific in if, like one of mine is and none of this works I am a little ashamed to say that I shoved my hand to the back of his throat when he mouthed me once and he never did it again. But this is last resort.
What's the thinking on puppies mouthing? When we visited Fitz at the weekend he was having a lovely time exploring dd's hands by licking and mouthing them. There was absolutely no pressure from his jaws and his mouth felt as soft as butter. Watching him with his litter mates they were all doing the same to each other.
Obviously we don't want him to grow up still mouthing things and people but I've seen a couple of conflicting bits of advice as to how to achieve this. Unless I'm completely misunderstanding, the kikopup videos say you should never ignore mouthing as that's reinforcing biting but I've seen a couple of other things which say that this phase is essential in developing a soft mouth. Which approach is right?