Research Findings: The present study describes developmental trends in false belief (in other and self) in 46 Mexican-dialect Spanish-speaking children from lower socioeconomic backgrounds with and without language impairment (LI). Results indicate that typically developing children's performance on false belief tasks improves with age, with very few 3-year-old children, half of the 4-year-old children, and most 5-year-olds demonstrating false belief understanding. Results also reveal that children acquire false belief in other in advance of false belief in self. Although there were no group differences between 3- and 4-year-old typically developing and LI children, there were significant differences in false belief performance between the 5-year-old typically developing and LI children. Practice or Policy: Implications for screening and enhanced false belief teaching strategies are presented. (Contains 3 tables and 2 figures.)