I witnessed a large white Shepherd/Chow mix maul a 6-year-old when I was about 8 or 9. The kid needed plastic surgery and everything.
A neighborhood puppy, Ginger, had started her first heat cycle and all the neighborhood dogs started following her around.
The attacking dog, Blitz, was normally inside a fenced-in back yard but managed to jump the huge gate when he got a whiff and joined the others for the next couple days. He was easily the biggest and fought away any other dog that tried to mount the puppy.
He was normally friendly to people but when the kid bent over to hug the fluffy puppy that was in heat, instinct took over and he treated the kid no differently than the other dogs messing with his girl.
I recall having to write my first witness statement and helping animal control hunt down the attacking dog, who was still friendly and happy to see me while we coaxed him into the trap. I later found out that the kid claimed that "the white dog bit me on the head and the brown dog bit me on the nose" so they both got put down. I'm pretty sure the brown dog (Ginger) only licked him/the blood after the attack, but neither should have been loose in the neighborhood.