If they want to be Cinderella, Tangled or Anna then the official Disney Store options are over priced but worth the extra cost if you can manage it. The cheaper options amiable on Amazon and in other department stores are half the price but you get what you pay for.
If you're looking for something less branded there are lots of wonderful options, and here are just a few.
Wonderful natural toy company Myriad have a beautiful Role Play section filled with multicoloured silk outfits, headdresses and playclothes. These wings are really beautiful but the skirts, dresses and crowns are also special additions to anyones dressing up box.
And who can resist a unicorn!
In my opinion a tutu is an important addition to any little girl's wardrobe and they're now available everywhere from markets and Etsy to Gap and H&M.
I particularly like the ones from children's fairytale party company With Love Crafts.
And for the ultimate tutu indulgence for those that don't mind blowing nearly £50 on their little fairies are these amazing flouncy fluffy skirts from Bodie and Fou or Trotters.