Now mostly superseded by its diminutive form baby. Used figuratively for “a childish person” from 1520s. Meaning “attractive young woman” is 1915, college slang. Babe in the woods is from 1795.
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.