Background: Paediatric delirium (PD) is increasingly recognised as a common disorder in critically ill children with a reported prevalence ranging from 9% to 66%. We validated the PD component of the Sophia Observation withdrawal Symptoms-Paediatric Delirium (SOS-PD) scale in a Danish setting to provide increased awareness and reliable identification of this critical condition, thereby paving the way for improved pathways to targeted delirium care. Objective: The objectives of this study were to criterion validate the PD component of the SOS-PD screening tool by comparing blinded psychiatric and nurse assessments and to estimate the prevalence of delirium in critically ill children in a Danish context. Methods: A prospective observational study was performed on critically ill children aged between 3 m and 18 y, admitted to an intensive care unit, with a hospital stay of 48 h or more. Assessments took place on a fixed weekday over an 18-month period. To test accuracy and criterion validity, bedside nurses’ SOS-PD assessments were compared to the reference standard, a diagnostic assessment performed by a child psychiatrist according to the Diagnostic and Statistical Manual-V criteria by use of the Vanderbilt Assessment of Delirium in Infants and Children. Results: We included 141 children in the study, 30 (21%) of whom were diagnosed with delirium by the child psychiatrist. The accuracy of the delirium diagnosis was 93.6% (95% confidence interval [CI]: 88.3–97.1) among the nurses’ SOS-PD assessments compared to the reference standard. The SOS-PD demonstrated a high sensitivity of 83.3% (95% CI: 65.3–94.4) and a high specificity of 96.4% (95% CI: 91.0–99.0) with five false-negative and four false-positive cases. Conclusion: The PD component of the SOS-PD tool has good accuracy and validity for assessments performed by nurses compared to a child psychiatrist's diagnosis in critically ill children in a Danish setting. We recommend the use of the SOS-PD instrument in clinical practice.