Evidence about the cost-effectiveness of interventions in children’s services can help decision-makers make more efficient use of scarce resources. We returned to six somewhat disparate interventions on which we had collated research evidence identified by service planners and practitioners as relevant to the well-being of children in the course of the Economic and Social Research Council-funded What Works for Children project. These are home visiting, parenting, cognitive–behavioural therapy, mentoring, traffic calming and breakfast club interventions. We aimed to explore the nature and extent of evidence on cost-benefit and cost effectiveness for these measures. We conducted searches for studies that looked at the costs as well as the effectiveness of the six interventions and found 24 studies matching our inclusion criteria. The studies were diverse in terms of study design and economic methods (including economic modelling and willingness to pay). Studies relating to parenting programmes and traffic calming gave the most positive indication that the interventions may be cost-effective for the outcomes in question. The remainder of the studies did not give a clear picture, in large part because of a lack of demonstration that the intervention was effective.