Research Findings: This study investigated the sequential mediating effects of parental material investment (MI) and time investment (TI) upon the correlation between family socioeconomic status (SES) and toddlers' development (TD). Data derived from a 2016 data set, including a sample of 1,316 toddlers based in 117 villages across 22 counties within northwestern China, were utilized. Parents completed the Bayley Scales of Infant and Toddler Development III (BSID-III) and Ages & Stages Questionnaires: Social-Emotional (ASQ: SE). The mediation analysis revealed: (1) a significant positive correlation among family SES, parental material investment, time investment, and the development of toddlers aged 0-3 years; (2) family SES indirectly impacted toddlers' development through the singular mediating pathway of material investment significantly, and the single mediating path of time investment was found to be insignificant; and (3) both material investment and time investment were recognized as the sequential mediators between family SES and toddler development. Practice or Policy: The study's findings underscore the aspects of parental material and time investment that optimally support toddlers' development. These results may also guide the structure and implementation of family interventions and policies designed to reduce the developmental disparity among toddlers from families of differing SES.