The United Nations Children's Fund says a child in a developing country who is breast-fed is almost three times more likely to survive infancy than a child who is not breast-fed.

The U.N. Children's Fund says under-nourishment contributes to about half of all deaths of children under five in the developing world. UNICEF spokesman, Patrick McCormick, says mother's milk can give a child a good start in life. He says breastfeeding is a very simple way to save children's' lives.

"Mother's milk is much more nutritional than any sort of formula invented," he said. "It has been proven time and time again that a child who is breast-fed will grow up taller, better and healthier, be more immune to diseases than a child on formula."

This week is World Breastfeeding Week, and marks the 25th anniversary of the international code of marketing of breast-milk substitutes. The code aims to protect and promote breastfeeding.

The World Health Assembly adopted the code in 1981 to counter an aggressive marketing campaign by companies trying to sell their infant formula to poor women in developing countries. Health experts say infant formula is less beneficial than mother's milk and can be deadly in areas where clean water is scarce.

McCormick says breastfeeding in most cases is best. However, he says there are times when that is not possible.

"The worst scenario is if the mother is HIV-positive and, in this case, obviously the mother is given the information to make a choice whether to breast feed or not. This may result in the child being HIV-positive, but not 100 percent of the time. Studies have been carried out which show that statistically the child will still have a better chance being breast-fed," said McCormick.

UNICEF says an estimated 63 percent of children less than six months of age are still not adequately breast-fed. As a result, it says millions of children start their lives at a disadvantage.

To date, more than 60 governments have enacted all or many of the provisions of the code as law. But, monitoring of code violations is weak in some countries.