Green’s Dictionary of Slang

(Irish) a term of endearment to a young boy, occas. to an animal.

1939		(con. 1880–90s) S. O’Casey I Knock at the Door 109: Good kidger, good kidger, called out the drover happily. [Ibid.] 116: Then, too, they had a mortal dread of the protestant Bible, the plain word of God, easy understood, even be kidgers.
1942		(con. 1890s) S. O’Casey Pictures in the Hallway 43: We’re leafin’ the kidger here for a few seconds.