The doctors and scientists streaming into the booth at the allergists' convention were amazed at what the middle-schoolers had wrought. The concept captivated them. It was a handheld scanner that could instantly translate confusing food labels to reveal potentially dangerous ingredients. For the 11 million Americans with sometimes lethal food allergies, it could prevent injury or even death. That it was invented by a bunch of kids barely into their teens only fueled the fascination last month for the annual meeting of the American College of Asthma, Allergy and Immunology. But dozens of would-be buyers of the "allergen scanner" were...