Dietary supplements —a broad term that includes vitamins, minerals, herbs, botanicals, probiotics and amino acids— are big business. The $26 billion industry has grown by 27 percent in the last five years. Pediatric supplements are a $573 million chunk of that, according to Euromonitor, a market research firm. The most popular supplement is the vitamin category. Researchers at U.C. Davis Children’s Hospital have estimated that one-third of U.S. children take some sort of daily vitamin.