When my DD was 7 we went and I needed something easy to pack and cool so she went as a Mexican girl. Wore lite weight white pheasant shirt you know the type with the elastic and sleeveless but has the ruffle around neck and over shoulder, bright color cotton full skirt I think red or orange (I made easily with elastic waist) and a sash around her waist (strip of bright striped fabric) and we put a couple tissue paper type flowers in her hair that I attatched to barrettes.
She looked very cute was cool, comfortable, could move easily, wore sandals, didn't take up a lot of room and inexspensive.