The dog acted properly in charging at the cops. The dog was acting in legitimate self-defense against an unjust aggressor. The cop is responsible for whatever happens when he shoots the gun.
The reason for the call is irrelevant. The kids were not holding a gun.
Reason NOT to call the cops.
Some stranger coming into the dark house with a flashlight and the kids are scared, my dog better go at him. Good dog. Bad cop.