For young children, sleep is essential for healthy development. Inadequate sleep can affect emotional, behavioural, cognitive, and health outcomes. Low family income and resources can put children at risk for poor sleep quality, impairing their subsequent cognitive abilities. The current study examined low socioeconomic status (SES) as a factor that increases vulnerability to the negative effects of poor sleep quality on young children's executive functioning (EF). It was hypothesized that sleep quality would be more strongly associated with EF skills for children from low-SES homes than for children from high-SES home. Results indicated that low family income predicted poorer performances in working memory. In addition, sleep quality was associated with working memory, but only for children from low-SES homes. These results suggest that sleep quality may be especially important for EF skills for children from low-SES homes.