In June, my oldest daughter declared that she was going to be purple butterfly while the baby was going to be a pink flower. She knew what she wanted!
I made a basic peasant top out of a green polka dot fabric for the flower costume. I used the same concept only bigger and longer for the butterfly dress. I have made these tops before: see here. They are super easy to sew up. I used Martha Stewart's idea for my youngest's costume. The leggings are from Old Navy. The petals are made from pink fleece and sewn onto a ribbon. So the petals are basically a ribbon necklace that can be easily removed (which ended up being a good thing because she hated wearing them).
The wings use the same fabric as the dress along with some teal and white felt. My inspiration was from these make these wings a few years ago for her monarch butterfly costume along with this lady's shop. She make absolutely gorgeous wings. My pale in comparison. Anyway, my daughter was thrilled and received lots of candy that night so she's happy.
side note: Her tights are from Target.