Cotton candy is made almost completely from sugar, with a few extras like dye and flavor. So it shouldn't be a surprise that cotton candy can can form crystals.
When cotton candy is made, it's melted into noncrystalline strands of caramelized sugar. But after we smashed it into a ball, washed it and let the water dissolve out some of the sugar, collected the sugar in a puddle, and let the puddle dry, small crystals started to develop in the center.
We had to throw the experiment away because my 4-year-old kept trying to lick it. But next time I get some cotton candy, I'll have to dissolve it, and see if I can get any crystals to grow.