He is just a baby so he is just playing. The growling and biting is just puppy play! I totally understand how you are feeling. I picked Cooper out because he was a spunky curious dog and after I bought him a few weeks later I was wondering "what did I do" I was wondering if I chose the right pup! I have a 7 year old and a 2 year old. & yeara old could defend herself pretty well but she did get a few good bites on her. My 2 year old is another story! I felt so bad for him Cooper would bite him so hard and make him bleed. Some of the bites were really deep and bled a lot! I would sometimes put Cooper in his Kennel to defuse the situation. He will grow out of this. Around 4 months old he will start losing his baby teeth and let me tell you his adult teeth are NOT the knives his baby teeth are. Cooper settled down a lot after he started losing his teeth to. He is now 7 months and a lover...he is such a chill relaxed dog and I am so happy I have him. This is just a phase one thing I would suggest is tell you kids not to run from him because it eggs him on more and he thinks they are really playing then he may aready be chasing them when your children run from him! The bigger he gets the worse he gets because he is going to be able to take your kids down. But like I said he will grow out of it. I would put my hand around his mouth closing it shut and say no biting or I would tap him on the nose with 2 fingers say NO NO No biting!!!Just keep up doing what you are doing making sure he knows it is not acceptable behavior. Gracie never went through the biting stage, I mean she would do her randoms playing bites here and there but nothing like Cooper! Coop still will have his days where he will bite or nip the kids but it is just puppy play! He has learned the soft biting play as well but sometimes he will get carried away and bite a little hard. Just keep and eye on your pup and correct him when you need to!