On November 5, 2007, a nanny left 4-year-old Tori Whitehurst of Maricopa County in her backyard with her 6-year-old sister and four dogs. One of the dogs killed the little girl by biting her on the neck. For more, see the article.
Multiple dogs in their own backyard without the presence of their owner — this is a common and dangerous scenario. Look at my dog bite danger scale, which is on the home page of Dog Bite Law.