Growing up, I always called adults as "Mr./Ms. <Surname>" (and until eighth grade, "Mrs." unless they specifically requested I call them by their first name. And even now, in my (almost.) mid-twenties, I still do that. I even use "sir" and "ma'am" unironically. Dan's right, I think, in that kids should learn to give due respect to their elders, and when I have tots of my own, I'll teach them what my parents taught me.