There are some awfully good suggestions here. I agree with Malinda in that when I got Maggie home, about 3 weeks into it, I wondered "What the hell were you thinking?!" I thought too that I was in way over my head and I'd never get Maggie trained or housebroken. I was miserable for a couple of weeks UNTIL I got a copy of "The Culture Clash" by Jean Donaldson (available at most bookstores online for about US$15). It saved my sanity and Maggie is so beautifully behaved now I can hardly believe she's the same little biting, growling, barking, peeing and pooping little dog I brought home at 8 weeks old.
I highly recommend getting a copy of this book, reading it and applying the techinques taught therein.
As for all the things you describe, they seem to me to be very typical Boxer puppy behaviors. Yes, they bite because they are teething and that's the way they play with other pups. You have to teach them when it is appropriate to bite, what is appropriate to bite and how to "soft bite." There is ample material available on the internet on soft biting that you should be able to find a method that works for you. I used the walk away and ignore her plan when she bit me. I'd just make a loud "OUCH" and get up and walk to another room and ignore her for a few minutes until she "got it" that when she bit me, play stopped. It worked very well.
One other thing to remember: These things take time. Your teaching the dog not to bite or jump on the kids will take time and patience and consistency on the part of EVERY MEMBER OF THE FAMILY. This is extremely important because the dog has to learn where it stands in the "pecking order" and all humans, even the kids, are higher on the ladder than the dog.
Don't throw the baby out with the bath water just yet. Just be patient and persisent and in a few more weeks you'll see real improvement in your pup's behavior. Boxers are extremely smart and quick to learn if you are teaching them correctly.
Good luck and keep us posted.
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Dan from Brooklyn
Proud Pappa to Maggie Mae, Born 6/16/00
Flashy Fawn (Red), docked tail, natural ears.
Pictures:
http://maggie.artshost.com