You seem to be assuming that everyone is well-versed enough in dog behavior to be able to educate their kids. There are a lot of people who have never owned a dog. Are they just SOL? I'd bet it fairly likely that the kid who was attacked in the video is unlikely to ever want to own a dog in the future. For those people who are unfortunate enough to not have an expert like you around to educate them, maybe there should be mandatory courses in school to teach kids how to protect themselves from being harmed by somebody's dog.
For me, I don't worry about dogs in my neighborhood. If a dog in my neighborhood would start acting aggressive toward me or kids, I'd just call the sheriff and insist that the dog is either kept chained up to protect me and others from it, or put down if it actually ever connects tooth to skin.
Instead of requiring innocent bystanders to learn to protect themselves from being attacked by your dog, it should be the dog-owners responsibility to educate their dogs that "play" like that is not allowed. Jail time for failure to responsibly manage their dog would work for me.
On further viewing, ‘d say the dog probably thought the kid was another dog. Usually, your first warning of aggressive behavior will result in a bite. And, usually, it will be precipitated by the bitten, whether they know why, or not. Do you let your kids play in traffic? Would you let them get hit by a car to make your point?
Pits are known to attack with no prior warning or history of shown aggression. Training children to read dog behavior won’t work because pits have had standard aggressive dog behavior bred out of them so they “surprise attack” often without snarling, barking, growling etc. There are videos just like the one on this thread where the pit bounces up wagging its tail before it starts to kill. Dogs do know how to play with one another and with people and it doesn’t involve stripping flesh or grabbing and shaking like a rag doll. That pit knew it was trying to sever limbs and enjoyed it so much that it wags its tail while doing so. Put the bystanders into a state of shock.
Here’s an example: https://www.youtube.com/watch?v=EBrFAbLOv4A
Searching Youtube for “pitbull attacks little girl” renders too many gory results to mention.