There's definitely a mister equivalent, least round here. Though I am not in the south, it's a thing. I've seen it most often with a parent or caregiver (not the kid's parent) speaking to them. I see it more of sign of respecting the kid a bit, as Max loves it. But we also encourage him to use mr. or ms. for grow ups, whether its last name or first (pending the grown ups prefence). So my friend joy becomes ms joy to him, and she calls him mr. Max in return.