SYNOPSIS: Objective. The objective of this study is to determine caregivers’ knowledge about when children begin to demonstrate basic cognitive, social-emotional, and motor milestones in three ethnic groups in Trinidad and Tobago. Design. Using the developmental niche model, a cross-sectional design was used to assess caregivers’ knowledge about when preschool-aged children begin to demonstrate basic developmental milestones in 1,117 African, Indo, and mixed-Caribbean ethnic groups from diverse socioeconomic backgrounds. Results. Caregivers had the greatest success in identifying linguistic and cognitive milestones. There were few differences in caregivers’ ability to accurately identify developmental milestones that were attributed to socioeconomic, maternal age, or number of children in the household. African Caribbean caregivers were more successful at identifying academic developmental milestones than Indo and mixed-ethnic caregivers. Indo and mixed-ethnic caregivers were similar in their ability to correctly identify, and in earlier expectations of developmental milestones, compared with African Caribbean caregivers. Conclusions. There were marked ethnic but few socioeconomic differences in caregivers’ knowledge about when children begin to demonstrate basic developmental milestones. Data have implications for childhood development and developmental surveillance in developing nations of the Caribbean.