Sleep loss alters processing of emotional stimuli in preschool‐aged children. However, the mechanism by which sleep modifies emotional processing in early childhood is unknown. We tested the hypothesis that a nap, compared to an equivalent time spent awake, reduces biases in attention allocation to affective information. Children (n = 43; M = 55.40 months, SD = 8.05 months) completed a Dot Probe task, which provides a measure of attention biases to emotional stimuli, following a mid‐day nap and an equivalent interval spent awake. No emotional attention biases emerged when children napped. However, when nap‐deprived, children exhibited biases towards negative and positive stimuli. This emotional bias after wake was greater in children who napped habitually. Gender differences also emerged such that females were more attentive to positive emotional stimuli whereas males showed heightened attention to negative emotional stimuli, regardless of having napped or not. Moreover, greater slow wave activity (SWA) during the nap was associated with faster responding, which suggests that SWA may promote efficiency of attention allocation. A video abstract of this article can be viewed at: https://www.youtube.com/watch?v=JIoZ8mzxQgg To understand the mechanism through which sleep alters emotional processing during early childhood, we assessed attention biases following a mid‐nap and an equivalent interval of wake in preschool children. Naps reduced emotional attention biases that were present following nap deprivation. Slow wave activity (SWA) may be a physiological property underlying the efficacy of emotional attention processing following sleep.