CHICAGO - The percentage of American children who are overweight or obese appears to have leveled off after a 25-year increase, according to new figures that offer a glimmer of hope in an otherwise dismal battle. "That is a first encouraging finding in what has been unremittingly bad news,'' said Dr. David Ludwig, director of an obesity clinic at Children's Hospital Boston. "But it's too soon to know if this really means we're beginning to make meaningful inroads into this epidemic. It may simply be a statistical fluke.'' In 2003-04 and 2005-06, roughly 32 percent of children were overweight or...