Caregiver knowledge of early child development (ECD) may shape the developmental opportunities available to young children, yet few measures assess this knowledge during the preschool years, particularly in low- and middle-income countries (LMICs). This study developed and psychometrically evaluated the Caregiver Knowledge of Early Child Development Inventory (CKECDI) and examined associations between its domains and preschool children’s executive and motor functions in Nigeria. In Phase one, 517 caregivers completed the CKECDI. Exploratory factor analysis (n = 259) and confirmatory factor analysis (n = 258) supported a 35-item, four-factor structure comprising cognitive development, socioemotional caregiving, school readiness, and health, nutrition, and safety. The four-factor model demonstrated good fit (CFI = .994, TLI = .994, RMSEA = .013, SRMR = .078), with acceptable internal consistency across domains (KR-20 = .74–.90; ω = .74–.89). Known-groups validity was supported by significant differences in domain scores across caregiver educational attainment. In Phase two, the CKECDI was administered to an independent sample of 286 caregiver-child dyads. Adjusted path analyses showed distinct associations between CKECDI domains and children’s inhibitory control, working memory, cognitive flexibility, and motor function. The CKECDI provides a multidimensional assessment of caregivers’ knowledge of preschool child development in LMICs and may support developmental assessment and research in culturally and contextually diverse settings.