Much malnutrition may be 'hidden', says Unicef
A total of 150m children can be defined as suffering from malnutrition, says the Unicef report.
However, the vast majority do not look like the media images of starving children often used to represent the problem.
In fact, most malnourished children do not show such distinctive signs of the condition.
Importantly, many children become malnourished in their first few years of life - when their brains and bodies are at key stages of development.
Often, lack of food is not the problem, but recurrent illness which stops the body absorbing vital nutrients.
Diarrhoeal disease and vomiting are commonplace among children in the developing world.
Fundraising programme
The Unicef report was published on Wednesday to coincide with a fundraising initiative, the Western Union Bright Futures Initiative.
An initial target of 1m euros (£619,000) has been set, and the money will be used to pay for Unicef's Early Childhood Development projects.
Roger Moore, the actor recruited as a "goodwill ambassador" for the charity, said: "The greatest tragedy of malnutrition is that it prevents children from reaching their full potential.
"We have made important strides in our understanding of nutritional health and it's crucial that individuals, governments, international agencies and donors rally to fully commit to early childhood development."
The report did contain some good news about progress in the fight against malnutrition.
Widespread deficiencies in vitamin A and iodine have been addressed by supplementing household salt with these - more than 70% of the developing world now uses salt with these added ingredients.
In addition, the proportion of women breastfeeding their babies has also risen slightly, from 40% to 45%.
There is plenty of evidence that this helps children ward off infection and provides essential micronutrients.