Some dogs think they are going to be aggressive with cats. Others bark hysterically in the car when they see a dog. You will hate this over the years, stop them when they are puppies. This is more than puppy rudeness, this is control. You are the leader of the pack.
All family members are to be respected.
No growling or aggressive behavior can be tolerated toward any small or helpless person or animal. Just follow the routine above more intensely. There are some good training tapes out for puppies. One is excellent. Dr. Ian Dunbar's Puppy Training.