Introduction: The Children’s Chelsea Critical Care Physical Assessment tool (cCPAx) is a measure of physical function for use in the paediatric intensive care unit (PICU). Growing evidence supports the efficacy and safety of early mobilisation (EM) in the PICU, yet there is a paucity of validated tools to effectively evaluate physical function and mobility in critically ill children. The cCPAx was developed using an iterative Delphi consensus method involving an expert panel to examine content validity and adapt the adult Chelsea Critical Care Physical Assessment tool for paediatrics.