Children who nap beyond the age of two may have poorer sleep quality overall, a new study suggests.

The length and quality of sleep toddlers get over a 24-hour period has a major impact on their health and development. By the time a child is two, they are usually getting most of their sleep at night, however many still have daytime naps as well.

Australian researchers set out to assess the impact of daytime napping on the quality of toddlers' sleep, as well as the impact on physical health, behaviour and cognition.

They analysed 26 relevant studies on napping in children up to the age of five and found consistent evidence which suggested that children who napped beyond the age of two took longer to fall asleep. These children also tended to sleep less at night overall.

The researchers were not able to find any definitive links between napping and behaviour or overall health.

They called for further research to assess the changes in sleep patterns in children during early childhood. However, they also suggested that if a pre-school child is having sleeping problems at night, their daytime sleeping routine should be considered as a possible cause.

"The impact of night sleep on children's development and health is increasingly documented, but to date there is not sufficient evidence to indicate the value of prolonging napping, whether at home or in childcare contexts, once sleep has consolidated into night," the team from Queensland University of Technology said.

Details of these findings are published in the journal, Archives of Disease in Childhood.