Some girl costumes are very feminine, and allow the child to dress as a beautiful princess. Frilly Disney Princess costumes are a good choice. This year, Elsa, the princess from Disney’s Frozen, is likely to be the most popular, since the Frozen theme remains extremely popular. But, the traditional Disney Princesses are all immensely popular, so Cinderella, Snow White, or any of the others can be chosen if the child has a favorite princess.
One thing any princess costume does is allow for a certain amount of bling, accessories that sparkle. There must be a tiara, and a wand can be a nice touch. Some fake jewelry can really make a child’s day fill with excitement.
Frozen actually offers two costume choices, Elsa and Anna, which works well for siblings who are close in age. Elsa is the more significant character, and the older of the two, but a younger sister may be happy dressing as the younger character, Anna. And, since the two characters are sisters, might just be delighted to play the part to her own older sister. Just make certain this is fine with the two children, especially if there is a sibling rivalry. You might just have to find two costumes of equal statue.