Objective: The objective of this study was to examine the relationships between sleep and attention in both typically developing (TD) children and children with ADHD. Method: The current study examined sleep and attention in 50 children, from 6 to 12 years of age (25 ADHD, 25 TD). Attention was measured using the Conners’ Parent Rating Scale–Revised: Long Version and the Attention Network Test–Interaction (ANT-I), which provided an objective measure of alerting, orienting, and executive attention. Sleep was objectively measured using actigraphy. Results: Children with ADHD had poorer alerting and executive attention on the ANT-I, as well as poorer parent-reported attention. In addition, poor sleep predicted performance on alerting attention for children with ADHD and TD children, whereas the interaction between poor sleep and ADHD diagnosis predicted executive attention scores. Conclusion: The findings of the current study highlight the importance of ensuring children are getting good quality sleep to optimize attention, particularly for children with ADHD.