This article addresses the issues in measuring pain in critically ill children, provides a comprehensive review of the pain measures for children aged between 0 and 3 years, and discusses their applicability to this group of children. When children are critically ill, pain can only exacerbate the stress response that already exists, to the extent that homeostasis cannot be maintained. Severity of illness is thus likely to affect physiologic and behavioural pain responses that would normally be demonstrated in healthy children. The problem of differentiating pain from other constructs adds to the complexity of assessing pain in non-verbal children. A pain measure to be useful clinically must be adapted to the developmental age of the target population. Search of electronic databases and other electronic sources was supplemented by hand review of relevant journals to identify published and unpublished pain measures for use in children aged between 0 and 3 years. Twenty eight pain measures were identified in the literature; 11 for neonates only, 11 for children aged between 0 and 3 years, and six for children more than 12 months. These measures vary in relation to their psychometric properties, clinical utility and the context in which the study was performed. These measures may not be suitable for the critically ill young child, because the items included were derived from observations of healthy or moderately sick children, and may not reflect pain behaviour in those who are critically ill. It is therefore recommended to develop new pain scales for this population of compromised children.