I've known her since she was 'a babe in arms'. [=a baby who is carried in the arms of an adult; an infant]
When I began my political career, I was a mere 'babe in the woods'.
Hey 'babe', how've you been?
(..) I get up at the crack of dawn always. Up the mountain, down the slopes, on the piste. You must be a very good skier. Well, I started when I was a mere babe in arms. I could ski before I could even crawl. Terribly sorry. I beg your pardon. It's all right. This hotel is deteriorating rapidly. (..)1975 The Return of the Pink Panther