Parenting, Eating and Activity for Child Health (PEACH) is a multi-component lifestyle intervention for families with overweight and obese children. PEACH was translated from an efficacious randomised-controlled trial (RCT) and delivered at scale as PEACH Queensland (QLD) in Queensland, Australia. The aim of this study is to explore pre-post changes in parenting, and child-level eating, activity and anthropometry, in the PEACH QLD service delivery project. PEACH QLD enrolled 926 overweight/obese children (817 families). Pre-programme evaluation was completed for 752 children and paired pre-post-programme evaluation data were available for 388 children. At baseline, children with pre-post-programme data were (mean) 8·8 years old, and at follow-up were 9·3 years old, with mean time between pre-post-programme measures of 0·46 years. Outcomes reflected each domain of the PEACH programme: parenting, eating behaviour of the child and activity behaviours (means reported). Parents reported improvements in parenting self-efficacy (3·6 to 3·7, P=0·001). Children had improved eating behaviours: eating more daily serves of vegetables (2·0 to 2·6, P=0·001) and fewer non-milk sweetened beverages (0·9 to 0·6, P=0·001) and discretionary foods (2·2 to 1·5, P=0·001). Children spent more time in moderate-To-vigorous physical activity (86 to 105 min/d, P=0·001) and less time in sedentary screen-based behaviours (190 to 148 min/d, P=0·001). Consequently, there were significant improvements in mean BMIz (-0·112; P<0·001) and weight status (healthy weight/overweight/obese/morbidly obese prevalence from 0/22/33/45 % to 2/27/34/37 %, P<0·001). When delivered at scale, PEACH remains an effective family-based, multi-component, lifestyle weight management programme for overweight and obese children whose families engage in the programme.