With many children and young adolescents reporting strong emotional bonds with their pets, the impact of pet ownership on child/adolescent health-especially on their emotional development-has garnered increasing scientific interest. We examined the association between pet ownership in toddlerhood (age 3.5 years) and poor emotional expression in later childhood (age 5.5 years) using propensity score matching within a longitudinal cohort dataset from Japan (n = 31,453). A propensity score for pet ownership was calculated by logistic models based on a comprehensive list of each child's observed characteristics, including sex, household income, parental education, mother's employment status, residential environment, number of siblings, and living arrangement. Log-binomial regression analyses using matched samples revealed that children who owned pets during the toddler years were 6% less likely to have a poor emotional expression in later childhood (prevalence ratio = 0.94, 95% confidence interval = 0.90⁻0.99) compared to those without pets. This suggests that owning pets may provide children with opportunities to control their emotions, and lead to a lower prevalence of poor emotional expression. Pet ownership in toddlerhood may contribute to the development of expression.