Fist, I am so sorry this happened to the kids pets. I can't even begin to imagine how they feel.
This is the GSD's owner fault, not the GSD. This is a breed with prey drive; with training they can ignore; without training some can ignore, others can't.
Nothing can replace the pets that your kid's have lost. I would be insisting on proof of training for the dog, current training not past training, INSTANT repair of the fence then also reinforcement of the full fence and raised to a height of 8 foot or more. At a time of your choosing, purchase of pets and hutch to not replace, but hopefully allow your kids to move on from this. This is a bare minimum. Some would even say to get AC involved. I am on the fence about that. If they refuse, then AC, insistence of the dog's rehoming or removal from property. This happened due to pure laziness and irresponsibility; both inexcusable.