One of the easiest, no-brainer costumes for girls that looks precious year after year is a princess outfit. To transform your little girl into a princess, all you'll need is a frilly dress, a tiara or headdress and a scepter. Costume jewelry, white gloves and slippers are optional add-ons. Premade princess costume sets are also easy to find. You can distinguish your princess by adding a set of wings and magic wand to the costume to make her a fairy princess, or you may want to pick out a specific princess character to model her ensemble after.