"For younger children, more explicit behaviours such as sharing and taking turns may be more important for friendships than subtle facial expressions. However, emotional expression becomes more important with age," explained Alfano. "Facial expressions not only provide others with an understanding of how you are feeling but are known to have a contagion effect on how others feel," she said. The results supported a burgeoning body of research that indicated poor sleep quality in childhood forecasts later socio-emotional problems and also indicated the importance of studies exploring how sleep affects multiple facets of children's mental health and well-being. Facial expression, a central aspect of social communication, is one aspect of emotion where sleep loss took a toll.