The ESCALATION system is a novel paediatric Early Warning System that incorporates family involvement and sepsis recognition. This study aimed to assess the feasibility and iteratively refine the ESCALATION system in a variety of hospital settings in preparation for full-service implementation. A series of four multi-methods studies using an Implementation Science and co-design approach were conducted. We examined concepts of implementation, context, and mechanisms of action across a variety of hospitals. Data collected included practice and chart audits, surveys (health professionals), interviews (families) and focus groups (health professionals). Quantitative data were analysed descriptively with qualitative findings assessed by content analysis or thematic analysis. There were 650 audits (Study I-IV), 205 health professional survey responses (Study I), 154 health professionals participated in focus groups (Study II-IV), 13 parents of hospitalised children interviewed (Study I), and 107 parents reported their involvement in the ESCALATION system (Study III-IV). Each of the studies further refined and confirmed the feasibility, specifically the components of family involvement and the sepsis recognition pathway. The Implementation Science evaluation of the ESCALATION system resulted in a uniform approach that was feasible and acceptable to users and appropriate for full-service implementation. This series of four studies used a co-production approach built on the Medical Research Council framework to understand feasibility and acceptability of an intervention to improve recognition and response to clinical deterioration in children to the point of full-service implementation. We have reported a detailed, systematic approach to assessing feasibility and acceptability of a complex intervention using established methodologies for whole of health system implementation. The ESCALATION System is an evidence based paediatric early warning system that is a highly refined, well accepted and accommodates a health system that has substantial contextual variation.