Disregarding my own persona as an “OC”
I give you these

I suppose you may be in luck

Reality changing zorua magick,

Or have I always wanted to be different Pokémon, yet I find myself unable to be everything at once

I suppose I always have wanted to be bigger in some regards. Be it power, size, or shape

No

To think my first guess could have won...
Ah, perhaps next time

Ah, a shame, I was going to say the slide, but I second guessed…

Mind if I rapid fire a few guesses?

A soccer ball was kicked into your leg

You fell off of an enclosure while playing, and hit your leg falling down.

You jumped off a tall height, to see how high you could land from

Ah, well, it seems partial credit follows me.
I believe I am out of guesses, then

Hmm, if I may take another guess, and seeing as many of the other attempts were you falling…
What if, it was something hitting your leg.
And seeing the playground being mentioned often, leads me to believe either a swing crashed into your leg, or perhaps somehting big and heavy fell onto you leg

Well, I suppose partial credit is deserved

I do not have much experience with broken limbs…
So I will not have much of a good guess. But, perhaps it was that you have tripped down the stairs. Or something involving you being distracted, and not watching where one walks