The core goal of paediatric palliative care (PPC) is to improve the quality of life (QoL) of children and their parents but defining and assessing this construct for children with life-limiting conditions is challenging. The objectives of this MOSAIK (Move to open shared advanced interventions for Kids with life-limiting conditions) research consisted in documenting the characteristics of children and their access to paediatric liaison teams (PLTs) in Belgium, adapting an instrument able to evaluate children’s and parents’ quality of life, assessing the psychometric properties of this instrument and analysing how its use was perceived among paediatric liaison teams. A systematic review looked at instruments used in PPC. We used a mixed-methods convergent triangulation design to confront the perspectives of children, parents and PLTs on their QoL. A pilot-test assessed the face and content validity, feasibility and acceptability of the further developed children’s palliative outcome scale (CPOS-2) in French. Finally, we conducted a multicentric national field-test among six PLTs, in French and Dutch, to document the reliability and concurrent validity of the CPOS-2, to provide an overview of children followed-up and to document the experiences of PLTs when using the CPOS-2. Results showed that more than 700 children /adolescents are referred to PLTs on an annual basis, but, between 2010 and 2014, only 1.7% of children facing complex chronic conditions and admitted to hospitals in the Brussels region had access to these. We also found a scarcity of outcome measurement instruments in PPC and that existing ones do not include children’s self-reports. Our study, conducted among 73 families, led to an adapted 20-item CPOS-2 able to evaluate children’s and parental quality of life (QoL), showing satisfactory reliability and concurrent validity. Quality of life scores do not seem to be linked to the severity of a child’s disease. Involving the main stakeholders during the whole process helped to develop a sound ...