another puppy is aggressive toward my puppy

Question
I have a 10-week old American Bulldog/Pitbull mix, and we are being very careful to socialize him with people and dogs.  My neighbor just got a 9-week old boxer.  We introduced them yesterday, and let them play together.  They played together fine until my neighbor let her other adult boxer out to play also.  Both puppies wanted to play with him, however, her puppy became jealous and attacked my puppy.  She then attacked him twice more.  The third time, he fought back.  How "dangerous" is this in his social development.  I do not want him to learn aggressive behavior.  Should I keep him from playing with the aggressive puppy?
Thank you.

Answer
Dear Angie,

Good for you proactively socializing your pup.  But you're right to follow your gut instinct and ask this question, and from what you've described I'd recommend you either ask your neighbor to let the pups play alone (without the adult boxer to be jealous of) in YOUR yard or a neutral place, until the pups are at least 5 months old.  Your little guy IS too small to be exposed to that kind of stuff, and although I am a firm proponent of pups being exposed to lots of different behaviors, the attacking seems to be a pattern and I wouldn't want him to start copying it.  

If your neighbors won't agree to that -- or if the boxer pup keeps up the attacking even without the adult around -- I'd socialize my dog elsewhere until he's a little older and has a solid core of happy social experiences to buffer any issues he may have with his neighbor pals.  Look for a positive, cage-free, reputable daycare in your area (try http://www.apdt.com for referrals) and pop in on them unscheduled to make sure they're keeping at very minimum a 1:15-20 human:dog ratio (no more dogs than that per person -- if there are more dogs than that per person, they can't properly make sure your little guy is having a positive experience).  

There may even be a place in your area where early puppy socialization classes are held ("puppy parties") or even an early puppy class where at least some off-leash play is allowed before, after or during each class.  If all that fails, check out dog parks in the area to socialize him but remove him if the play gets too aggressive.  And if that's not an option, just walk him 2-3 times daily around lots of people/kids/leashed dogs and try to bring him wherever you go.

Good luck and thanks for writing.
Suzanne Harris, BSc, CPDT
http://www.dogdaysUSA.com