I am very sorry Gunner was hurt
These little guys are so small and wiggly .Especially when they are excited. When Suzi was a tiny pup she nearly jumped out of my arms onto the sidewalk, I barely was able to catch her. IT haapens in an instant.
These accidents are not rare. A excited little puppy will literaly jump out of your arms and accidents happen. Give your daughter loves of hugs and reassure her that gunner is going to be ok. How is Gunner feeling tonight? Try to keep him calm and warm. Make sure he is eating and drinking well, and keeping warm.