I'm going to stick my neck out here but I wonder if one of the kids tease the puppy when it's trying to eat. I had a step-sister who when my parent's dog was trying to eat, would take her food away from her. Even though my parents would get after my step-sister, she kept it up. Finally, the dog got so no one could get near her when she was eating. She was the sweetest tempered dog you could imagine usually. It started with behavior like you described with the pup, a little nip because she thought the food was being taken away.

Maybe this is the pup for Aunt Jazz' parents? Just a thought.