In real life the last time I had a parent drive by was about a month before we moved out of the US--so about 13 months ago. I had taken the kids into work with me for my 4 hour shift at our small town library. They too ksome money and their cell phones and walked down to a local deli for lunch (and to bring some back for us librarians). It was a 5-10 minute walk which involved crossing only one street (our sleepy downtown, 25 MPH Main street with crosswalks) which took them past the police station and several stores whose owners we knew.
An accquaintance who had literally driven by them called the library concerned that I might not know my kids were out in town "all alone." I confirmed that they were behaving themselves and walking where they should have been and then asked her what the issue was

BTW the kids were 12 and 10 at the time.
I don't run into this at all here in Germany where most kids are very independent. However, I have been villified on the DIS a number of times for various parenting issues.
You sure do run into these kinds of parents a lot don't you? I think it was you who got yelled at for singing Trent Resnor sons with your DD also. Am I right? (BTW--I was one of the parents on that thread who does not censor music). Anyway, how i handle this in real life is generally just to either totally ignore the person or to calmly tell them that their concern is sweet but I am comfortable with my parenting choices while smiling at them. Kidness seems to disarm most people like this.
For the record, both of my children were using many public restrooms alone by the time they were four. I personally couldn't imagine sending them to school (they both started kindergarten at 4) if they could not handle a public typical public restroom on their own. As far a "busy" restruraunt is concerend--I actually think it is SAFER somewhere busy (with lots of witnesses) than in a quiet and isolated area.