Despite progress toward assuring the health of today's young population, the 21st century began with an epidemic of childhood obesity. There is general agreement that the situation must be addressed by means of primary prevention, but relatively little is known about how to intervene effectively. The evidence behind the assumption that childhood obesity can be prevented was discussed critically in this roundtable symposium. Overall, there was general agreement that action is needed and that the worldwide epidemic itself is sufficient evidence for action. As the poet, writer, and scholar Wittner Bynner (1881–1968) wrote, “The biggest problem in the world could have been solved when it was small”.