Phrase(s): A babe in the woods
Fig. a naive or innocent person; an inexperienced person. (Like a child lost in the woods.) Bill is a babe in the woods when it comes to dealing with plumbers. As a painter, Mary is fine, but she’s a babe in the woods as a musician.
McGrawhill's American Idioms And Phrasal Verbs
An innocent or very naive person who is apt to be duped or victimized, as in She was a babe in the woods where the stock market was concerned. The term originated in a popular ballad of 1595, "The Children in the Wood," about two young orphans who are abandoned in a forest and die.
American Heritage Idioms