Fathers remain under-represented in early childhood obesity prevention research and interventions, despite growing evidence that paternal biopsychosocial factors and behaviors from pre- and post-conception can influence lifelong offspring health. Informed by a literature review of high-quality evidence, "CO-Parent" (childhood obesity-Parent) is a new conceptual model underpinned by couple interdependence theory and a socioecological framework. Literature was searched for the concepts parental AND weight-related behaviors AND child weight or weight-related behaviors, in databases including MEDLINE, PsycINFO, Global Health, Scopus, and SocINDEX. Prior evidence syntheses were prioritized as source data to inform model development. "CO-Parent" illustrates the interdependent and independent effects of maternal and paternal weight, weight-related behaviors, and well-being, across preconception, pregnancy, postpartum, and the early years on child weight-related behaviors and weight up to age five. The influences of public policy, social, environmental, economic, community, and other complex modifiable mediating factors are included in the model. The "CO-Parent" conceptual model paves the way for a paradigm shift by recognizing fathers as key figures in early childhood obesity prevention initiatives, encouraging them to "share the motherload." It highlights both the independent and interdependent roles fathers play in the epidemiology of obesity starting from preconception. CO-Parent also provides the foundations necessary to guide future theory and research to be more inclusive of fathers to further understanding of the independent and interdependent influences of parents in early childhood obesity prevention.