This paper describes how children’s needs are routinely ignored or misunderstood by urban development policy, plans and practice – and the very high costs this brings for them in terms of ill-health, injury, premature death and impaired physical, mental and social development. For instance, provision for water, sanitation and housing often fails to address the main requirements for child health while neighbourhood-wide development fails to understand the significance of play for children’s development, including the extent to which adequate provision reduces accidents. The impact on children of evictions, overcrowding and neighbourhood violence is also considered. The paper also describes, with examples, how acting on children’s needs and priorities can be incorporated into existing interventions without major cost increases, and the benefits this brings for children and for other inhabitants.