Kellogg's, Kraft and Quaker Oats have followed General Mills in raising prices. Kellogg's, the world's largest cereal maker, on Monday raised prices for its ready-to-eat cereal range, the first such change in eight years. The move could be a chance for Kellogg's to break out of a spiral of declining margins in its most important market, but doubt remains as to whether the US cereal market has really turned the corner.