Materials:
One roll of Cotton quilt batting, pink dye, white tights or leggings, pink turtle neck, pink thread pink or other light colored beanie for cap. Duct tape or super sticky 2 sided tape.

Unroll the batting and as loosely as possible put it in the washing machine, fill will the hottest water setting possible. As you're adding the water, add the dye. I used powdered RIT dye from the supermarket but liquid dye works well too. Add vinegar or salt if the directions on the package call for it. Put the machine on gentle cycle and allow it to swish around for a few minutes. You can check the color every few minutes. When it is the color of cotton candy switch the machine to the spin cycle. Hang the cotton batting over a couple of chairs or a clothes bar to dry, it may take a few hours.
This costume is kind of made on the kid.
When dry, tear into strips so the edges look thin and ragged like real cotton candy.
Wrap the batting around the dressed child, so it resembles cotton candy. You can use pink thread to tack it in place in some spots so it stays put or use rolled duct tape underneath.
For the hat;
I made it by sewing small strips around a beanie cap that I had crocheted in pink yarn. It would work equally as well and be much faster to use a cheap beanie hat from the dollar store or an old one, I would use a light color though because it may show through the batting if it is too dark.
If you don't want to sew, double sided tape or rolled duct tape may work as well. Just keep adding small strips around making the ends puff out like the top of cotton candy.
Some pink sparkling shoes and pink cheeks and your cotton candy cutie is ready to go!