Childhood obesity remains a significant public health issue. Because lifestyle behaviors and weight are established early and track through life stages, prevention strategies must commence in the first years of life. Traditionally, such strategies target parents or formal child care providers. Yet grandparents are increasingly providing care to grandchildren and therefore have an important role in their eating and activity behaviors, which creates a major research gap. This commentary piece, focusing on the Australian context, argues that it is imperative and timely for obesity prevention research to include investigations regarding the role of grandparents in the prevention of obesity-related behaviors in young children.