This study investigated the development of multitasking ability across childhood. A sample of 65 typically developing children aged 7, 9, and 11 years completed two multitasking tests across three time points within a year. Cross-sectional and longitudinal data consistently indicated continuous linear growth in children's multitasking ability. By the age of 12 years, children could effectively perform a simple multitasking scenario comprising six equally important tasks, although their ability to strategically organize assorted tasks with varied values and priorities in a complex multitasking setting had not reached proficiency yet. Cognitive functions underlying a complex multitasking scenario varied in their developmental trajectories. Retrospective memory developed continuously from 7 to 12 years of age, suggesting its supporting role in the development of multitasking. Planning skills developed slowly and showed practice effects for older children but not for younger children. The ability to adhere to plans also developed slowly, and children of all age groups benefited from practice. This study offers a preliminary benchmark for future comparison with clinical populations and may help to inform the development of targeted interventions.