Definitions by Bia is me

Hey Kiddo 

A phrase, used occasionally when greeting, someone within a close proximity to your own age (1 day-1 year).
Used more frequently by a non-relative when greeting a (friend's possibly) child.

Katie: (to Jeff) "Hey Kiddo"
Jeff: "Oh shut the hell up I'm only 3 weeks younger than you"
Katie: "Still fucking younger kiddo"

or

Old guy: "Hey Kiddo" (some form of annoying touching i.e. cheek pinch)
Teenager: "WTF?!?!"

Hey Kiddo by Bia is me January 6, 2006