Neuroimaging the sleeping brain: Insight on memory functioning in infants and toddlers

•Episodic memory develops considerably during infancy and the toddler years.•Development of the hippocampus is hypothesized to be critical.•In vivo investigation in humans has been limited due to methodological challenges.•Functional MRI increasingly used in early childhood and can image the hippocampus.•Functional MRI data promises to connect brain and memory development at this age.