Background Duration and quality of sleep affect child development and health. Encouragement of napping in preschool children has been suggested as a health-promoting strategy.

Objectives The aim of this study is to assess evidence regarding the effects of napping on measures of child development and health.

Design This study is a systematic review of published, original research articles of any design.

Subjects Children aged 0–5 years.

Method Electronic database search was performed following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and assessment of research quality was carried out following a Grading of Recommendations, Assessment, Development and Evaluations (GRADE) protocol.

Results Twenty-six articles met inclusion criteria. These were of heterogeneous quality; all had observational designs (GRADE-low). Development and health outcomes included salivary cortisol, night sleep, cognition, behaviour, obesity and accidents. The findings regarding cognition, behaviour and health impacts were inconsistent, probably because of variation in age and habitual napping status of the samples. The most consistent finding was an association between napping and later onset, shorter duration and poorer quality of night sleep, with evidence strongest beyond the age of 2 years.

Limitations Studies were not randomised. Most did not obtain data on the children's habitual napping status or the context of napping. Many were reliant on parent report rather than direct observation or physiological measurement of sleep behaviour.

Conclusions The evidence indicates that beyond the age of 2 years napping is associated with later night sleep onset and both reduced sleep quality and duration. The evidence regarding behaviour, health and cognition is less certain. There is a need for more systematic studies that use stronger designs. In preschool children presenting with sleep problems clinicians should investigate napping patterns.