Tho IAAL, this is not my specialty, so I will flaunt my ignorance.
Also, these are my personal views rather than any description of laws or liabilities.
Each case certainly needs to be examined on its own merits. In a case where the dog is in a fenced, marked yard, I think some degree of contributory negligence should be relevant for all but the absolutely youngest victims (maybe 3 or under? Or maybe 5 or so when they should be able to read.) What responsibility does a parent have to teach their kids to respect other peoples’ property? Or to teach a kid to avoid dangerous situations? Don’t play in the street. Don’t go into a yard where you know there is a dog. I understand that increasing levels of responsibility kick in as age increases, tho reflect a child’s maturing ability to reason. IMO, “Dogs might bite” is just about as basic as “Don’t touch the stove, it might be hot.” Yeah, it sucks that accidents happen and kids burn themselves and try to pet “the pretty doggie.” But that doesn’t mean someone should necessarily be held liable.
Of course, I believe the degree of injury and the individual history of the dog should come into play.
A case close to me involves my neighbors. Their youngest kid was bitten by dogs 3 times before she was maybe 5 years old. Each time the kid had gone into a fenced yard she was not invited into. Each time the dog’s owners were liable for expenses, and one dog was put to sleep. I am terrified that this little creep will come into my yard, do something to my sweet dog, and get bitten, with unpleasant consequences. Now that she is about 8, I hope she is more respectful of people’s property and the potential implications of her actions. But we were very clear with both her and her folks that she was under no conditions welcome in our yard uninvited. They recently got a puppy. I believe it is just a matter of time …
The discussion of “Who needs xyz breed of dog?” reminds me of lots of the gun debate. “Who needs xyz weapon?” Whether you view it as fortunate or unfortunate, this seems to be a result of our desire for relatively unfettered freedom of individual choice.
Finally, I agree that the distinction between crim and civ liability is important. Just about anyone can sue you for just about anything that is arguably related to something you own or control. As you go through your life, you make your choices as to how you style your life. Those choices have potential implications. If you install a pool, whatever precautions you take, it is more likely that a kid will drown in your backyard than if you do not have a pool.
Same with dogs. If you have a 200# dog that you are not physically able to control, it is more likely that your dog will cause serious injury than if you have a chihuahua.
Of course those are extremes. But if you choose to own a breed that has a bad rep - whether you think that rep is deserved or not. Or if you choose to keep a dog that has shown aggressive tendencies in the past. Or if you let the dog roam unleashed. Or leave it in the yard unattended when you know there are kids around. You made those choices and must live with the potential implications.