Despite the incompatibility of ontological and epistemological assumptions underlying quantitative and qualitative research, combining both research traditions are often recommended to advance our understanding of research questions. This paper draws on my mixed-methods doctoral study to address a substantive question—the influence of parental migration on left-behind children’s (LBC) nutritional health in rural China. This paper has demonstrated why and how a mixed-methods research design was chosen and processed in order to advance the current debate. A longitudinal data analysis of 975 children is integrated with a qualitative study of in-depth interviews with 32 caregivers on caregiving practices for 26 children (21 LBC and five non-LBC) who were encouraged to keep diaries of their everyday lives. The juxtaposition of both elements shows negative associations between parental migration, especially maternal migration, and LBC’s nutritional outcomes, and this is particularly true for boys left behind during their early life due to specific sociocultural factors in rural China.