Background: Delirium commonly occurs in paediatric patients with acute critical illness and negatively affects clinical outcomes. Variations in delirium knowledge levels and its management have been noted among nurses. Aims: This study investigated nurses' experiences and knowledge levels regarding paediatric delirium. Additionally, we aimed to assess the gap between knowledge levels and practical experiences with paediatric delirium. Study Design: This cross-sectional descriptive study conveniently sampled paediatric nurses from a university hospital in South Korea between September 2022 and March 2023. Nursing experiences with paediatric delirium and delirium knowledge levels were measured using structured survey questionnaires. Delirium knowledge was scored 0 to 47, and higher scores indicated higher levels of delirium-related knowledge. Data were analysed using descriptive statistics and presented as mean, standard deviation, frequency and percentage. Results: A total of 127 paediatric nurses participated in this study; 40.2% had experience with 1–5 delirium cases in the previous year, and 86.6% (n = 110) had never used assessment tools for paediatric delirium assessment. The mean total delirium knowledge score was 34.45 ± 5.4; the mean scores of knowledge regarding aetiology, signs and symptoms and nursing management of delirium were 8.93 ± 1.31, 13.24 ± 2.81 and 12.3 ± 2.7, respectively. Interventions associated with a lower level of delirium-related knowledge and a lower performance rate included avoiding restraint use and maintaining hydration and electrolyte levels. Interventions associated with a higher level of delirium-related knowledge but a lower rate of performance comprised providing orientation, offering emotional support, allowing participants to stay with family members and administering medications to manage delirium. Conclusions: Although nurses working in paediatric units exhibited high rate of delirium nursing care, there was the gap between their delirium-related knowledge and practice. Nurses need to be aware of the insufficient part of delirium care, and paediatric delirium education should be reinforced. Relevance to Clinical Practice: Preventing, assessing and systematically managing paediatric delirium is crucial, and considering the study results, delirium education among nurses is needed.