Pneumonia
According to some research in 2010, in some parts of the world where people are very poor like India, Nigeria, and Pakistan, pneumonia was the cause of death for more children under the age of five than any other disease.  Statistically, however, for every 2,000 children in the developing world who die of pneumonia, only one child in the developed world dies from the disease.  This is because of differences in health care and because of differences in rates of breastfeeding, not because of differences in children.  Breastfeeding newborn babies greatly increases their ability to survive pneumonia, but some cultures think of breastfeeding as taboo.