INTRODUCTION: Paediatric sepsis is a major contributor to morbidity and mortality worldwide. Assessing concern from parents and healthcare professionals to determine disease severity in a child evaluated for sepsis remains a field requiring further investigation. This study aims to determine the diagnostic accuracy of parental and healthcare professional concern in the diagnosis of children evaluated for sepsis. METHODS AND ANALYSIS: This prospective multicentre observational study will be conducted over a 24-month period in the paediatric emergency department (ED) at two tertiary Australian hospitals. A cross-sectional survey design will be used to assess the level of concern in parents, nurses and doctors for children presenting to ED and undergoing assessment for sepsis. The primary outcome is a diagnosis of sepsis, defined as suspected infection plus organ dysfunction at time of survey completion. Secondary outcomes include suspected or proven infection and development of organ dysfunction, defined as a Paediatric Sequential Organ Failure Assessment Score >0, within 48 hours of presentation, paediatric intensive care unit admission, confirmed or probable bacterial infection independent of organ dysfunction, and hospital length of stay. ETHICS AND DISSEMINATION: Ethics approval was obtained from Children's Health Queensland's Human Research Ethics Committee (HREC/17/QRCH/85). Findings will be shared with relevant stakeholders and disseminated via conferences and peer-reviewed journals TRIAL REGISTRATION NUMBER: WHO Universal Trial Number, U1111-1256-4537; ANZCTR number, ACTRN1262000134092.