Definitions for kiddoˈkɪd oʊ
Random House Webster's College Dictionary
kid•doˈkɪd oʊ(n.)(pl.)-dos, -does.
Informal. (used as a familiar form of address.)
Origin of kiddo:
1880–85; kid1+ -o
An affectionate moniker for a close friend or pal, especially used as a form of address.
Okay, kiddo, I gotta run.
Origin: Probably derived from kid, an informal term for child. Appears to be colloquial in United States and Canada.