Do you think it is okay for kids to greet adults by their first name?

In our house it's Sir or Ma'am

I do not use first names unless encouraged to. At Uni, professors use first names and I still cannot seem to do it, I prefer "Prof. or Dr." My students call me "Dr.___"

There are parents who insist that their children address all adults as Mr./Miss/Mrs. So-and-so, no matter what.

So their child meets a new adult. "Pleased to meet you Mr. Jones."

"Call me Fred," Mr. Jones replies.

"Yes Mr. Jones."

"Seriously, I prefer to be addressed by my first name. Please call me 'Fred.'"

"Yes Mr. Jones."

And this is supposed to be all about "respect??"

Children have always called me by my first name and I'm fine with it.

I don't think being made to address adults as Mr/Ms So-and-So makes children respect that adult any more than if they used the adults' first names. I know there were adults I addressed "respectfully" as a child whom I thought were stupid and/or bullies etc.

absolutely. My name is Jorge nothing before or after.

Mr or Mrs or Miss. Or Sir and Ma'am, which I was taught

I always tell em ta use Chris not one fo formalities

Depends on the situation. First meeting respectful, then can call by first name in non formal settings.