I don't know what the etiquette of this is. But I think it's futile to talk to the parents. If they cared how their child behaved out in the neighborhood, they would have either trained him, or they would watch him. They didn't even train him to watch for cars, or better yet, not to ride his scooter in the STREET. Do you think they care he is frightening your dogs or might be bitten?
Your best bet is to be firm with the child, as another poster suggested. In very uncertain terms, forbid him to come near you or the dogs. If he keeps coming, you turn around and go the other way and report an unsupervised child who is always playing in traffic. Don't mention your dogs, just say that you see him out there all the time and you're afraid he'll get run over, so the cops might actually follow up.
He doesn't sound quite right, to me. He's not picking up any of your cues or verbal instructions. Either no one ever gives him any kind of instruction, or he's incapable of understanding it the way you've been putting it to him. Speak loudly and firmly and turn around if he doesn't listen. Don't walk on that street if you can't get it through his skull. It's not worth the risk to your dogs. If that kid gets bitten, mommy and daddy are suddenly going to care a whole lot about the kid's safety, and your dog could end up paying the price.