Background <p>Childhood obesity is a global health challenge, with physical inactivity as a key driver. Digital health interventions (DHIs) may increase physical activity (PA) among children and adolescents with obesity. This umbrella review aimed to evaluate the effectiveness and sustainability of DHIs in improving PA in this population.</p> Methods <p>An umbrella review was conducted in accordance with the Preferred Reporting Items for Overviews of Reviews statement. Systematic reviews assessing DHIs, targeting PA outcomes among children/adolescents with obesity were included. Reviews were identified from five databases. Data were synthesised narratively, with effect sizes interpreted based on the Cochrane guidance. Risk of bias was assessed using the AMSTAR 2 tool.</p> Results <p>Nine reviews were included. Overall, DHIs were found to produce small to moderate improvements in PA. Text messaging demonstrated modest effectiveness based on meta-analytic evidence (SMD = 1.011, 95% CI: 0.251–1.771), while exergaming interventions showed favourable effects in narrative syntheses. Sustainability data were limited. Seven reviews were rated as critically low quality.</p> Conclusions <p>DHIs showed small to moderate improvements in PA among children and adolescents with obesity, a finding supported by lower-quality evidence.</p> Limitations <p>The evidence was limited by methodological flaws, inconsistent reporting of outcomes, and insufficient indicators of sustainability.</p> Registration <p>PROSPERO CRD42024611938.</p> Impact <p><UnorderedList Mark="Bullet"> <ItemContent> <p>This umbrella review summarises evidence on the effectiveness and sustainability of Digital Health Interventions (DHIs) for increasing physical activity among children and adolescents with obesity.</p> </ItemContent> <ItemContent> <p>It adds to the literature by evaluating both intervention outcomes and behavioural implementation features.</p> </ItemContent> <ItemContent> <p>The findings support the design of sustainable, equitable, and effective DHIs as part of childhood obesity treatment strategies.</p> </ItemContent> </UnorderedList></p>