The "fairy" being an airborne thistle seed, or the parachute left over after the seed has gone.
I first heard this tradition in NZ in the 90s from my mother, but a bit of internet searching pulls up results from the UK and Australia. At my school, you'd say your wish over it then release it without damaging it, but a minority believed you had to tear off one of its bristles.
Assorted traditions characterize supernatural beings as being able to grant wishes, but this is usually accomplished with some coercion (often with the entity's capture). These stories usually don't end well: the person manages to win his wishes, but they typically backfire in some unpleasant way.
When authors adapted these sorts of legends for children's literature, the dangerous elements of these encounters were typically softened, so that all remained was the delightful potential of the supernatural to grant wishes. The thing I'm not sure about is whether there was a child's tradition that predates these publications. That's possible and it would be interesting to delve into this, but I do not know of any evidence for this. I suspect that the child's tradition was influenced if not created by by the publications, but that may not be the case.
