This report describes the relationship between sleep and cognitive function in children. As reviewed, the empiric data to directly address the effects of sleep loss or disruption on children's cognitive function are quite sparse. However, a wide range of clinical and observational data support a general picture that inadequate sleep results in tiredness, difficulties with focussed attention, low threshold to express negative affect (irritability and easy frustration), and difficulty modulating impulses and emotions. In some cases these symptoms may resemble attention deficit hyperactivity disorder. These findings are discussed in relation to a model of sleep loss influencing prefrontal cortex including executive functions involved in the control of attention and emotions.