If I had a kid who was killed by other kids...
...even in the circumstances shown in this film, I'd seriously consider killing them. However, I think I'd just torture them but keep them alive. Don't worry not like Saw, but in a sociopathic way. I'd kinda' do what Two Face (forgot his name) did to start with. Visit and just scare them verbally and show photos and stuff. Then I'd start doing loadsa' scary $hit... don't know what really. But no way would I let them get away with it. Even if they were like 8 years old. Any younger than 8 I suppose I would, as kids as young as that can't really contemplate such things.
...let's try and, let's try and, let's try and... let's make this precious!