The new short film “Blue Bonnets” celebrates a treasured cultural pastime in Scotland that, for its young performers, is simply dance. “My favorite dance is the jig, and my second favorite is the Blue Bonnets,” Victoria, one of the children whom we see practicing their steps, tells the camera. No adult appears in the film, and childlike spaces—a tufty lawn, a swing above a river, a faded gym hall where girls sit gossiping in corners—abound. “I was quite interested in the idea of practice and ima