A front-page exposé in yesterday's New York Times reveals that schools across America are serving students canned and frozen vegetables. The authors, reporter Elizabeth Becker and food writer Marian Burros, seem confident that kids would eat more-balanced diets if only these "tasteless" side dishes were replaced with fresh, flavorful produce. But while adult palates might appreciate steamed rapini tossed with olive oil, balsamic vinegar, and crushed red pepper, the average 8-year-old does not. If anything, he prefers his vegetables tasteless, which is not to say that he particularly likes them either way. This is a perennial challenge for parents trying to make sure their children get adequate nutrition, and it is not likely to be solved by the new federal guidelines in which Becker and Burros put their hope.