There's two huge problems right there in bold. One, dog owners who own questionable breeds can never let the animal out of their control, even accidentally.
And two, chasing the dog was the exact wrong thing for the kids to do. Many dogs, even mellow breeds, won't take kindly to this and may try to defend themselves. Kids will be kids, but as parents we need to try and educate them about not chasing/cornering/accosting strange animals, particularly dogs.
LQ