As far as opening lines go, it's the opposite of original. It's formulaic and trite. But it's also a ritualistic opening that cues the reader into a familiar state of expectation.
On one of my first ever visits to The Strand (I have vague memories of cutting my afternoon solfège and composition classes at music school and taking the subway downtown - notable because it was my first time taking the subway alone), I found the unedited versions of the stories of The Brothers Grimm and Hans Christian Andersen. I was both horrified and fascinated to learn that Cinderella's stepsisters had cut off their toes and heels so that they could fit their feet into the slipper, and that they were found out only when their bloodied white stockings were noticed and pigeons came to pluck out their eyes.
And thus, for their wickedness and falsehood, they were punished with blindness as long as they lived.But the story that captured my imagination and broke my heart was Andersen's The Little Mermaid. For those of us who watched the Disney version, we know the story. A beautiful young mermaid princess saves the life of a young human prince and falls in love with him, and trades her voice for legs.
But what Disney edited out, was that part of the spell that required the little mermaid's tongue to be cut off, and that while her legs were beautiful and her gait graceful, every step she took felt as though she were walking on countless knives. And, of course, that the feckless prince chose another to love. (Men. SO typical.)
Bruno Bettelheim, in his book, The Uses Of Enchantment, writes that children can well tolerate such violence and evil, because it affirms their understanding of and satisfies their desire for justice. Good triumphs and is rewarded. The evil are horribly punished.
I don't know anything about child psychology. Hell, I don't know anything about children at all. And I read the original versions of these fairytales when I was around 12, not 5, so I can't even point to my own experience and claim that as a small child I wasn't adversely affected by the brutality.
So I'll content myself with saying that as an adult, I wait, with great expectation, for the terrible beauty and fierceness that follows the words: "Once upon a time..."