Smkie,
You keep saying how a 5 year old should know that it is unacceptable to hit dogs but be rational-
You KNOW that kids, especially that young, are not going to listen well. You tell them to clean the room, do they do it? No. You tell them not to hit the dog? But they think it's fun- so they continue, they get bit, and in turn the animal is put to sleep. It's not right, I know.
But you can't expect a 5 year old to be able to listen as well as a teenager. It doesn't work that way.
That's why, in my opinion, kids should be around dogs but under intense adult super vision. But even then it's hard not to prevent it, you could be in the same room working and concentrating on something else and the next thing you know your dog has your kid by the throat. It's why I emphasized intense.
Just my opinion.