Some packs are not properly socialized. And I think the Staffies and Pits have been so interbed/inbred that they are just dangerously unpredictable like this.
Even the Chihuahua has to adjust and get over some jealousy when the grand baby first came around. But a PitBull is completely out of the question.
My miniature dachshund showed her disapproval of my newborn son by pooping under his crib.