AimWe evaluated the effect on body mass index standard deviation score (BMI‐SDS) of a combined treatment (Web‐COP) for children with obesity, including a web‐based component targeting their parents.MethodsThis randomised controlled trial recruited children 5–12 years of age with obesity (International Obesity Task Force BMI [IOTF‐BMI] ≥30 kg/m2) from school health care and outpatient paediatric clinics in in Northern Sweden from 1 June 2019 to 21 June 2020. The children were randomised to Web‐COP, an intervention with group sessions and a 12‐week web‐based component, or standard care. The primary outcome was the change in IOTF BMI‐SDS after 6 months.ResultsIn total, 75 children (33 girls), mean age 9.5 years, were randomised, and 65/75 (87%) children and their parents completed the study, 35/39 (90%) in the Web‐COP intervention and 30/36 (83%) in the standard care group. BMI‐SDS at 6 months was changed from 3.08 to 2.81 in the intervention group compared to an increase from 3.07 to 3.16 in the standard care group, representing a significant difference between groups (p < 0.001). In the intervention group, 14/30 (47%) reduced their BMI‐SDS ≥0.25, compared to none in the standard care group.ConclusionThe parent‐focused intervention significantly improved BMI‐SDS in children with obesity as compared to children in standard care.