Charles' research interests are in maternal and child 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 trial in Uganda of kangaroo mother care offered to low birthweigh neonates before stabilisation (the OMWaNA 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; the Kenyan district hospitals study to improve the quality of inpatient care for children; 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).

Charles' other research is at the National Perinatal Epidemiology Unit of the University of Oxford where he is a co-investigator in the Children's Surgery Outcome Reporting (CSOR) programme.