nonsense refrain in songs, probably from Old English la, a common exclamation; but la-la is imitative of babbling speech in many languages (cf. Greek lalage "babble, prattle," Sanskrit lalalla "imitation of stammering" Latin lallare "to sing to sleep, lull," German lallen "to stammer," Lithuanian laluoti "to stammer").
Examples from the Web for la-la
Meanwhile, returning from la-la land to our regularly scheduled program, 86 people died in the United States today from gunfire.The Fear About Things That Won't Kill Us Is Killing Us|Cliff Schecter|October 25, 2014|DAILY BEAST
When his literary ancestors attempted to conquer La-La Land, they were rebuffed, rewritten, or humiliated.‘The Counselor’ & How Cormac McCarthy Beat the Hollywood Curse|Andrew Romano|October 26, 2013|DAILY BEAST
"It becomes us to take care of the pence now," she would say, and go on with her everlasting whistling, La-la.
And I says 'see the nice gentleman's stick,' and she gurgles 'la-la!'
"Tra-la la la-la-la-la, la-la la," he sang, snapping his fingers.One Man's Initiation--1917|John Dos Passos
He was leaning his hands on his stick and she reached out and took hold of it and says 'la-la!'