When we think of a flamenco dancer, we think of her wearing something very colourful, very spotty with lots of frills around the hem and sleeves. This little cutie is wearing a perfect example - unfortunately, she hasn't quite got the steps yet...
In fact, this style of dress is rarely worn by flamenco dancers these days. You'll still see it in tourist venues and at the annual Feria in Seville, where it's traditional.
If you're in Seville and tempted to buy one, make sure you buy a dress for dancing and not just a Feria (or vestida de gitana) dress. Feria dresses are tight way down past the knees with just a few frills at the bottom, and there's not enough freedom of movement to dance properly.
A dress designed for professional dancers may look very similar, but it will only be tight to about mid-thigh. You'll also see full-skirted styles. You can see some examples in this video:
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Photo by qgil

Sevillanas is a folk dance of Seville and has nothing to do with flamenco dance except the geography. To lump the two together is like saying Cajun music and New Orleans jazz are a single genre because they originate in the same place.
You might see flamenco dresses worn by sevillanas dancers, but not sevillanas dresses (what the little girl in the video is wearing) worn by flamenco dancers.
Estela Zatania, editor
http://www.deflamenco.com/indexi.jsp
Of course, you’re absolutely right, Estela. However, like it or not, almost every flamenco dancer outside Spain will learn the Sevillanas as his or her first “flamenco” dance – and most people outside Spain think the spotted, frilly dress is what a flamenco dancer wears.