On May 3, ChopChop, a Watertown-based quarterly children’s cooking magazine, surprised the food world by winning the James Beard award for publication of the year. “It’s amazing and it’s been great to get that kind of acknowledgement,” says founder and president Sally Sampson. “You wouldn’t even think we’d be in the running.” Sampson, an author of 22 cookbooks who has contributed to the Boston Globe, launched ChopChopKids in 2010 with the goal of teaching children and parents to cook healthfully. While initially aiming to distribute solely through pediatricians during well-child visits, the magazine is now a fixture at food banks, schools, and medical offices, with an international circulation of about 2 million copies each year. Sampson says ChopChop is in roughly 50 percent of pediatricians’ offices. Last year, the nonprofit started a workshop at Harvard and it’s aiming to publish a magazine for a younger audience called ChopChop Jr.