Charles' research interests are in child and newborn health.

He has advised on and contributed to the design and analysis of a variety of studies. They include: a study developing and testing a new nutritional protocol for the treatment of acute malnutrition in children in Kenya and South Sudan (the ComPAS study); a study to reduce aggression and bullying to promote emotional health and well-being in secondary schools in England (the INCLUSIVE study); a study in Zomba Malawi to investigate the impact of a school-based programme of diagnosis and treatment of malaria on school attendance; a study to improve the health and survival of mothers and babies through generating evidence to inform policy and practice in Ethiopia, Nigeria and India (the IDEAs project); and a trial investigating the effect of lipid nutritional supplementation in addition to seasonal malaria chemoprophylaxis on morbidity and mortality of children in Nigeria (the SMaMP trial).

He is designing and testing novel approaches to measuring quality of care for children receiving in-patient hospital care, linked to work conducted in a cluster randomised trial in Kenya.

Charles' other research is at the National Perinatal Epidemiology Unit of the University of Oxford. He is exploring the impact of fathers' involvement on the psychosocial development of children in the Avon Longitudinal Study of Parents and Children (the ALSPAC Fathers study), and the role of social deprivation in explaining variations in health outcomes in infants.