Through selective breeding, humans have created different breeds of dogs that have genetic predisposition for specific tasks. The AKC has grouped dogs into seven groups. I have trained and shown Australian Shepherds and Golden Retrievers in the AKC Obedience ring. Pit Bulls, German Shepards, Dobermans, etc. have a genetic predisposition to be very protective of their "pack".
The problem is NOT with the dog. It is with the owner who does not know how to train their dog. I have seen this time and time again.
If you cannot train a dog, how can you train a child?