This study aimed to identify critical features of successful lifestyle weight management interventions for overweight children (0-11years). Eleven qualitative UK-based studies examining children's, parents' and providers' perspectives and experiences of programmes were synthesised to identify components felt to be critical. Studies for this views synthesis were identified from existing reviews and an update of one review's search, which was run in December 2015. The identified components were then explored in a synthesis of intervention evaluations (five 'most effective' and 15 'least effective') conducted in western Europe, North America, Australia or New Zealand. The intervention evaluations were identified from existing reviews and an update of one review's search, which was run in March 2016. This evaluation synthesis was carried out using Qualitative Comparative Analysis. Three important mechanisms were present in all the most effective interventions but absent in all the least effective: 1/ showing families how to change: a) providing child physical activity sessions, b) delivering practical behaviour change strategy sessions, c) providing calorie intake advice; 2/ ensuring all the family are on board: a) delivering discussion/education sessions for both children and parents, b) delivering child-friendly sessions, c) aiming to change behaviours across the whole family; 3/ enabling social support for both parents and children by delivering both child group sessions and parent group sessions. To conclude, programmes should ensure the whole family is on board the programme, that parents and children can receive social support and are not just told what to change, but shown how.