Early childhood development (ECD) is crucial for a child's future academic and social success. In Nairobi slums, where resources are limited, ECD programmes can significantly impact children’s early years. The study employed a longitudinal design with pre- and post-intervention assessments. Data were collected through standardised questionnaires administered to parents/guardians of participating children aged 0-5 years. A notable increase in cognitive scores was observed, with an average improvement of 12% compared to baseline measurements. The intervention programme demonstrated positive impacts on early childhood development across various domains. Recommendations for policy and future research are provided based on these findings. Policy recommendations include expanding access to ECD programmes in Nairobi slums, with a focus on socio-emotional skill development interventions.