In Katherine Mansfield's story "Her First Ball", the theme of the loss of innocence is treated by using contrast in the description of the different instances that bring out the natural spark of the girls attending a glittering, coming of age event as big as a first ball.
Mansfield is very liberal in making charming and nouvelle observations that clearly reflect the innocence with which the girls approach the event:
Dark girls, fair girls were patting their hair, tying ribbons again, tucking handkerchiefs down the fronts of their bodices, smoothing marble- white gloves. And because they were all laughing it seemed to Leila that they were all lovely.
When Mansfield focuses on the seemingly magical light under which the ball develops, she accentuates the feelings of naivete, novelty, amazement, and awe of the characters.
She clutched her fan, and, gazing at the gleaming, golden floor, the azaleas, the lanterns, the stage at one end with its red carpet and gilt chairs and the band in a corner, she thought breathlessly, "How heavenly; how simply heavenly!"
Then, comes the contrast: Just as Leila, our main character, has absorbed from this experience everything that is beautiful, charming, and new, in comes the character of "the fat man". It is this character who gives Leila a sour dose of reality by relating to her, during the dance, the realities of life.
[..] you can't hope to last anything like as long as that. No-o," said the fat man, "long before that you'll be sitting up there on the stage, looking on, in your nice black velvet. And these pretty arms will have turned into little short fat ones, and you'll beat time with such a different kind of fan--a black bony one.
Already he is breaking up the fantasy that Leila had built at the sight of the beautiful setting, with the gorgeous ladies dancing to the fabulous sounds of the orchestra. Meanwhile, he continues with his ramble.
And you'll smile away like the poor old dears up there, and point to your daughter, and tell the elderly lady next to you how some dreadful man tried to kiss her at the club ball. And your heart will ache, ache.
After this dance, Leila wants to stop dancing. It is a metaphor for wanting to quit the joviality of youth and joy after one knows what lays ahead in life: Aging, deteriorating, and dying.
However, the importance of this incident is that youth is such a powerful time in life that it accentuates everything we see. Leila is one of such youngsters who can only exist in the moment and cannot bare the idea of a future less beautiful. This is what illustrates a form of loss of innocence, or naivete, that surfaces for the first time this night, when Leila attends her first ball.