How do you know there attitude if you haven't talked to them? I don't know your beliefs.
I'm a Christian and I don't think killing someones dog, basically destroying taking there property is a very good testimony. They may need to hear about my savior and this could just open the door, it doesn't carry much weight if I just blew a crater in their kid's pet.
If it is the kids pet they should care enough about it to keep it up and protected. Its not my kids pet I keep mine up. I give dogs multiple chances and take them back to the owner but after 2 or 3 chances it is yoyr responsibility to keep up with your dog not mine