Sounds like you may be in the UK?
I am very sorry about your pets. That is a horrible thing - when I was a little girl, 2 American Bulldog type dogs came through and killed almost all of our chickens, rabbits and ducks. It was awful. Whoever allowed them to run was at fault.
I am still unsure in my feeling brain what to think when animals just kill to kill, and have a dog who is much like Lenny in Of Mice and Men and likes to kill anything that squeaks in the yard (fine with my inside cats) then seems sad that they don't play anymore. In my logic brain, they are animals.
If my dog did this, I would be replacing that fence, and providing you with some recompense for the animals and their housing that was destroyed.
I am sorry about your kids - the best thing that my family did was not let me see any of it up close. They also did not focus on the anger and upset, but what we could do to move forward. I think they were in shock too, and we also had no idea who owned the dogs.
If you know anyone else with dogs that are good with kids, I'd want to keep that in the back of my mind for the future, so that they can be around dogs in a good way, and also to look at the many things that the breed has done and been bred to do - herding, protecting, police, guide dogs, therapy work, and understand that sometimes a dog's animal instincts take over.
I really am sorry.