My set icebreaker-
Whenever I meet a child (4-8) I always say, How old are you, about_______? (add 2 or three years to the obvious). When they reply "6" for example, I add-"Oh I thought you were at LEAST 8 because of how grown up you act/look/talk etc.
They light up and grin from ear to ear, and become my new best friend!