The U.N. agency said a breastfed child in a developing nation is nearly three times more likely to survive infancy than a child who is not breastfed.
The report was released Tuesday, at the start of a weeklong commemoration of the most natural way to nourish babies.
"World Breastfeeding Week gives us an opportunity to advocate for a very simple way to save children's lives," said UNICEF Executive Director Ann Veneman. "Though breastfeeding rates are increasing in the developing world, an estimated 63 percent of children under 6 months of age are still not adequately breastfed. As a result, millions of children start their lives at a disadvantage."
World Breastfeeding Week -- observed in more than 120 countries -- promotes exclusive breastfeeding for the first six months of life.
Continued breastfeeding after six months, for up to 2 years of age or beyond, combined with safe and appropriate complementary feeding, is the optimal approach to child feeding, UNICEF officials say.
Dennis Rodman pledges to end trips to North Korea
Teacher apologizes for showing sexual image of herself in class