Catastrophizing about sleeplessness is a cognitive process associated with sleep disturbance in adults. This study aimed to (1) examine whether children catastrophize about the consequences of not sleeping; (2) define the topics that children catastrophize about; (3) assess whether there is a link between catastrophizing and sleep disturbance in children; and (4) examine whether an association between catastrophizing and sleep in children is mediated by anxiety and depression symptoms. Children completed the sleep self-report and a catastrophizing interview. Testing took place in two inner-city schools in London, UK and participants comprised 123 children aged between 8 and 10 years (49% male). Thirty-four (28%) participants reported concerns in response to the catastrophizing questionnaire. The main topics being catastrophized were concerns about sleep, physiological issues and one's own emotions. Catastrophes predicted sleep disturbance after controlling for age and sex (beta = 0.35, P < 0.001) but not when controlling additionally for anxiety and depression symptoms (beta = 0.15, P = 0.106). Symptoms of anxiety (Sobel test = 3.30, P < 0.001) and depression (Sobel test = 2.90, P = 0.004) mediated the influence of catastrophizing on sleep. A proportion of children catastrophized about the consequences of sleeplessness and this was associated with sleep disturbance, an association which was mediated through anxiety and depression symptoms.