FOR LOVERS OF HISTORICAL ADVENTURE, A FAMILY APART IS THE MIDDLE-GRADE ANSWER TO CHRISTINA BAKER KLINE'S NEW YORK TIMES BESTSELLING ORPHAN TRAIN. Imagine being taken from your home. Imagine your mother is the one who lets it happen. This is the fate that befalls the Kelly children. It’s 1856, and their widowed mother has sent them west from New York City because she’s convinced that…