Parenting responsibilities?

So, yesterday I pull into our neighborhood and saw one of my other friend's two year olds was in the road on his little gator. Check out this picture.

At this point, he was going down the road that goes to the right in this picture at the stop sign. I saw him turn the corner torwards his house, so I figured they were out for a walk and he was just behind. Ok, I can live with that.

Well, a few minutes later, he he comes down the main road that goes into our subdivision. Basically, he had gone through his yard and through another houses yard into the main road leading down to the stop sign. He was weaving around in the middle of the road and cars were trying to get around him. Now, our subdivision isn't small (I didn't draw all of it here) and we have close to 150 homes (not large either), but it was "rush hour" when everyone is coming home from work and such. I tried to call my friend whose kid it is and no one answers. So, I leave PM and DQ with C (whose house we were at, as I was dropping off her son) and walk over to get the little boy and walk all the way home with him. When I get there, his older sister, who will be 6 next month, was outside playing and says something to the effect of Braden, where were you? I ask her to go get one of her parents. My friend comes out and I tell her where he was. She says, oh he likes to ride over in front of so and so's house. I told her no, he was completely in the road and cars were trying to avoid him. She says, "B, you know you are not supposed to ride in the road" and that was it.

OMG! He is 2 for crying out loud. The kid doesn't even really speak and she is leaving him outside alone to fend for himself!!! I jokingly said B you better listen to mommy or she will take away your keys or lock you in the backyard, yes they have a fenced in backyard.

Ok, I can see leaving him outside while you make dinner, in the backyard with the fence shut if you can see him from the house. But, at 2, I don't even know that I could do that. I leave mine outside, in the fenced backyard while I make dinner, but I can see them and they are older. It still makes me nervous! (I know, I am a worry wart.)