I have 3 german shepherds. Due to prey drive they are never allowed contact with the chickens. They would not kill them intentionally, but the bite force thinking its a toy is enough. One of mine did get a baby rabbit. I never saw a dog move faster. He just walked around with it in his mouth, until I was able to get him to drop it. I was hysterical and will never forget it. It was nothing vicious either. As long as mine don't have contact they watch over them. There was a GSD near by that would chase coyotes off that tried getting chickens. Bunnies, squirrels and chickens are off limits, but I can tell you they adore kids and are good with people.
I'm very sorry for your losses. As a GSD owner I would be horrified if any of my dogs did that and I would pay all expenses without court, but that is who I am.