Undernutrition is prevalent among urban poor children in Democratic Republic of Congo (DRC), with limited data on effective nutritional interventions. A mixed-methods approach was employed, including dietary assessments, anthropometric measurements, and qualitative interviews to evaluate changes over time. During the intervention period of 12 months, participants gained an average weight increase of 0.5 kg compared to a control group (95% CI: -0.1 to 1.1 kg). Household food security statuses improved significantly from 40% pre-intervention to 65% post-intervention. The community-based nutrition programme showed promise in improving weight gain and enhancing household food security among undernourished children in DRC's urban areas, although the effect on weight was modest. Further studies should explore scalability and cost-effectiveness of this intervention model for wider implementation. Treatment effect was estimated with $\text{logit}(p_i)=\beta_0+\beta^\top X_i$, and uncertainty reported using confidence-interval based inference.