Malnutrition is the underlying cause of more than half of all child deaths, experts have warned.
Save the Children warn thousands of Sudanese children are at risk
As aid workers seek to avert a famine in Sudan, the World Health Organization said poor nourishment leaves children underweight and weakened.
This means usually non-fatal illnesses, such as diarrhoea, can kill them.
The American Journal of Clinical Nutrition study said giving all children an adequate diet could save over 2.5m lives a year.
The study said a million deaths from pneumonia, 800,000 from diarrhoea, 500,000 from malaria, and 250,000 from measles could be prevented.
Data from 10 studies of childhood deaths around the world was analysed, and complex formulas were used to extrapolate the effect of weight on the likelihood of death.
The researchers estimated that 52.5% of all deaths in young children were attributable to under-nourishment, with nearly 45% of measles deaths and more than 60% of deaths from diarrhoea associated with low weight and poor nutrition.
Laura Caulfield, an associate professor with the Johns Hopkins Bloomberg School's Center for Human Nutrition, who also worked on the study, said: "Malnutrition does not have to be severe to have a significant impact on child health and survival.
"Our analysis shows that even children who were small, but whose weight would not classify them as malnourished, were twice as likely to die as children in our reference group."
She added: "These findings underscore the need to make the improvement of the nutritional status of children a priority."
Rudy Von Bernuth, Save the Children vice president and managing director of emergencies and crisis, warned the current crisis in Sudan was likely to escalate over the next six months.
"We already are seeing very high malnutrition rates, especially among children.
"We are setting up emergency therapeutic feeding centres to help the most severely malnourished.
"The possibility of thousands of children dying of malnutrition and disease is very real."