Background Despite efforts to reduce under-5 mortality rates worldwide, an estimated 6.6 million under-5 children die every year. Community mobilisation through participatory women's groups has been shown to improve maternal and newborn health in rural settings, but little is known about the potential of this approach to improve care and health in children after the newborn period.

Methods Following on from a cluster-randomised controlled trial to assess the effect of participatory women's groups on maternal and neonatal health outcomes in rural Bangladesh, 162 women's groups continued to meet between April 2010 and December 2011 to identify, prioritise and address issues that affect the health of children under 5 years. A controlled before-and-after study design and difference-in-difference analysis was used to assess morbidity outcomes and changes in knowledge and practices related to child feeding, hygiene and care-seeking behaviour.

Findings Significant improvements were measured in mothers’ knowledge of disease prevention and management, danger signs and hand washing at critical times. Significant increases were seen in exclusive breast feeding for at least 6 months (15.3% (4.2% to 26.5%)), and mean duration of breast feeding (37.9 days (17.4 to 58.3)). Maternal reports of under-5 morbidities fell in intervention compared with control areas, including reports of fever (−10.5% (−15.1% to −6.0%)) and acute respiratory infections (−12.2% (−15.6% to −8.8%)). No differences were observed in dietary diversity scores or immunisation uptake.

Conclusions Community mobilisation through participatory women's groups can be successfully adapted to address health knowledge and practice in relation to child's health, leading to improvements in a number of child health indicators and behaviours.