War Horse is ideal material for Steven Spiel­berg. His adaptation of the children's novel by Michael Morpurgo comes to the screen by way of the celebrated National Theatre stage version, which has been entrancing audiences of all ages on Broadway since last season. It's the story of a magnificent auburn stallion named Joey, trained by a Devon farm boy, Albert Narracott, and then sold by his father to the army at the outset of World War I.