I've lived in neighborhoods where parents let their children, of all ages, run wild all over at all hours. Are these parents neglectful? Yes. Half the time they aren't even home.
But the neighborhood I live in now, children are allowed out to play. They play ball in the alley behind my house, they go the the nearby park on their own, they ride their bikes on the street, etc. They are well behaved, well loved children. I'm GLAD they are allowed to do these things. I think its good for them. I'm appalled at people who drive their kids two blocks to school because they are afraid something might happen. Something MIGHT happen (but it probably wont). . . and the kids need to grow up . . .and they need the excercise.
So our tendancy to scream "bad parent!" whenever something goes wrong can be dangerous in its own right. I remember several scrapes I got into as a child that had they turned out badly, and happened today, my parents might have been charged with endangerment and neglect. . . and I think I had good parents. I was just an independent, clever child. A generation ago . . . and even more so my parents generation, there was an understanding that accidents happen. Sometimes they are in fact the child's fault . . . sometimes they are no one's fault. Sometimes, in an otherwise safe sitaution, something goes wrong.
As for chldren getting into a dog's yard, I think we really need to look at the entire situation. How well marked was the yard? What was the child doing? Were there warning signs? How old was the child? What was the dog doing? There's a huge difference between a kid climbing into a yard with a high fence, with warning signs, and an obvious snarling dog, and a kid running onto a yard (with an invisible fence) to get a ball and a dog darting out from under the porch to attack him. Now, I'd say those cases are pretty clear cut . . .where it gets difficult, and where this law comes in, is where you have a normal garden three-four foot fence, no lock on the gate, no sign, dog is there but has never harmed anyone . . . barks, perhaps . . . kid's ball bounces in the yard, kid doesn't see dog, slips into get ball, dog walks around the house, sees kid and bites . . . I'd say that dog wasn't being "reasonable" and its owner is at fault . . for not locking the gate, for leaving the dog out when he wasn't at home . . . take your pick.
But another ambigious situation . . . same dog, same kid, same fence, same ball . . . the dog is visible, the kid comes in, sees the dog (who barks or growls), runs to get the ball, and then throws the ball at the dog's head. Perhaps the kid is scared . . . perhaps he's mean, doesn't matter. From the dog's perspective, an intruder has entered, been warned, and then attacked him . . . a nice bite on the leg is in order (but a mauling might not be).
But are the parent's at fault in either of these situations? Assuming they told the kid never to go in someone else's yard, probably not. The kid made the decision on his own to get his ball, even though it was against the rules. Kids do that.