Di'n' I tell you th'ee las' night?
Go 'way, honey, you ain't right.
I got somep'n' else to do,
'Cides jes' tellin' tales to you.
Tell you jes' one? Lem me see
Whut dat one's a-gwine to be.
When you 's ole, yo membry fails;
Seems lak I do' know no tales.
Well, set down dah in dat cheer,
Keep still ef you wants to hyeah.
Tek dat chin up off yo' han's,
Set up nice now. Goodness lan's!
Hol' yo'se'f up lak yo' pa.
Bet nobidy evah saw
Him scrunched down lak you was den--
High-tone boys meks high-tone men.
Once dey was a ole black bah,
Used to live 'roun' hyeah some whah
In a cave. He was so big
He is signifying that the boy is young by telling him to sit up in his chair like a man. Younger children often think of their father as their hero, so the narrator coaxes the boy into sitting up straight by telling him that his father would never slouch. 

A Cabin Tale