Congrats on your new puppy! Exciting!
We had "fun" with the puppy nipping and our daughter. That was definitely a challenge for a little while.
Your puppy should have NO unsupervised time with the kids. Hard, I know, but its really important. If young kids do not have the control or maturity to enforce good puppy behavior then they shouldn't be allowed to be around the puppy unless an adult is right there, preferably with pup on a leash.
When my pup was small we kept a leash on her whenever my daughter (same age as your kiddo) had friends over. We often did the same when it was just our daughter. The puppy seemed to sense that she was a "human puppy" and that she was ripe for play fighting. I'd clip the leash to my belt buckle with a carabeiner. (It helped great with potty training, too.)
Using the leash was the best way to keep the pup from getting carried away, and also to keep the pup from learning bad habits with children. We also trained our daughter to YIP as loudly and sharply as she could whenever the pup nipped, and then the pup went immediately into the crate. We had to do this until she was about 4 months old, but now at 8 months old she is GREAT with kids and never, ever uses her mouth with them.
You are also going to want to get your pup exposed to age-similar puppies ASAP for dog socialization and bite inhibition learning. Due to your dog's breed this is going to be especially important, as some of the bully breeds can become dog aggressive if not socialized to other dogs when very young.
At six weeks your puppy was really taken much too soon from his mama and litter-mates and this is really going to effect his bite and nipping, as well as his future behavior with dogs unless he gets lots puppy time within the next eight weeks.
Young pups have a very important "bite inhibition" period where they really need to have that rough play they get with their litter-mates. Puppy play teaches them how to gauge the correct pressure to use when mouthing. A puppy always uses its mouth when play-fighting, and when a litter-mate bites too hard the pup YIPS and quits playing. They learn that rough playing results in losing a playmate and learn to hold back their bite.
Someone I know adopted a 6-week Doberman pincher and it turned out to be a BIG problem; he was great with all people but very under-socialized to other dogs because of his early adoption. He had no bite inhibition. He ended up severely biting his "dog house-mate" during a play fight one day.
He'd never played with other pups and never learned to "hold" his bite.Edited by tinuviel_k - 3/16/11 at 4:41pm