Green’s Dictionary of Slang

a soothing excl. offered to a fallen child as one picks them up; a cry for anything about to rise up, e.g., a plane [? the image of plucking a daisy from a lawn].

1862		C.C. Robinson Dial. Leeds 442: Upsa daesy! a common ejaculation when a child, in play, is assisted in a spring-leap from the ground.
1890–1904		Farmer & Henley Sl. and Its Analogues.
1932		(con. WWI) L. Mann Flesh in Armour 159: He clambered out of the trench and gave his hand to his batman. ‘Upsadaisy!’.
1943		Bayler & Carnes Last Man Off Wake Island 90: [a pilot] ‘Upsydaisy!’ cried Elrod.
1943		I. Wolfert Tucker’s People (1944) 326: ‘Upsadaisy,’ said the manager. He put his hands under Wheelock’s arms and lifted him to his feet.
1972		M. Rodgers Freaky Friday 74: ‘Ups-a-daisy,’ I said, dusting myself off.