Plaid dress with pleated skirt for school. Saddle oxfords are the most popular shoe. All occaison coat, double-breasted, has the new back fullness. Her bag, like mother's, swings from the shoulder. Twin sweater sets, similar to those popular in colleges, are good for teenagers, too. Party dress of rose velveteen, feathered bonnet and a matching bag, make this young girl a perfect little lady. Siren effect produced by slinky black dress and up-hairdo is inappropriate. Single-breasted fitted…