At 5 months of age your puppy should be well on its way to learning bite inhibition. Most of the teeth should be in, and teething should not be much of a contributing factor. Use appropriate chew toys such as Nylabone products and real bones, such as those made by Red Barn. Do NOT use reprimands and do NOT squeal when the puppy bites. Rather, stop interaction in a matter-of-fact way. Resume after 15-30 seconds. When the puppy is mouthing, give it the chew bones to chew on instead. Do this in a matter-of-fact way. Sometimes puppies and adult dogs as well mouth for attention. Make sure you do not reward and reinforce this behavior by giving the dog attention for this behavior. Instead, give your puppy attention when s/he is not asking for it and reward sitting behavior with attention so that this becomes your puppy's default behavior to get attention Leave hard chew toys out at all times to satisfy your puppy's chewing urges. Supervise all interactions between your child and the puppy and discourage rough play which can excite the puppy and lead to biting.