You will get much advice, but just like with toddlers you will need to train them not to do this. This is usually a puppy's way of 'playing', but they need to understand that it hurts you. I am very dramatic. I don't just say Ouch, no.... I act like it is severely hurting me, accompanied with a human "YELP!" and then I will push them away, saying "NO BITE!!!" Once they understand this hurts you and it is not a good behavior, they should quit doing it. Other things you can use are cans of coins to shake, or spray with water bottle, or canned air.