Music and mathematics have been associated since Pythagoras, but there is limited evidence on whether musical engagement promotes the acquisition of cognitive skills in young children that support later learning of mathematics. The goal of the present study was to test if numerical cognition and working memory was enhanced in pre-schoolers who were actively engaged in music. The performance of two groups of children (aged 3 to 5) in numeracy, numerosity, subitizing, and memory tasks were compared. The children in the music group (n = 28) had participated in weekly 30-minute music classes for at least 6 months prior to the study. The control group (n = 28) were children attending regular preschools without any additional music classes. Older children (>= 4 years) performed significantly better than younger children (< 4 years) on most measures. A series of ANCOVAs with music group and age as factors and socioeconomic deprivation (NZDep) as a continuous covariate showed that the music group performed significantly better on several measures related to numerical cognition, including numerosity discrimination and subitizing with canonical (symmetrical) displays. Overall, these results provide evidence that musical engagement helps preschool children develop numerical cognition skills.