Over 200,000 children around the world die from cancer each year without ever receiving basic medical care or relief for their pain, a report says.
A lack of money prevents drugs getting to patients, say experts
The International Confederation of Childhood Cancer Parent Organisations and Cancer Research UK say more money is needed to tackle the problem.
The ICCCPO has written to UN Secretary General Kofi Annan demanding action.
The report is published to coincide with International Childhood Cancer day on Sunday.
Over 250,000 children around the world develop cancer each year. One in five of these live in developed countries.
The remainder live in the developing world where they do not have access to medical care.
Experts believe as many as 100,000 children could beat the disease if they received treatment.
"These children have a right to life," said Geoff Thaxter, vice-president of ICCCPO.
"If we can get the support of Kofi Annan and governments around the world, this can all be done more quickly."
Professor Tim Eden of Cancer Research UK said even a little extra cash can go a long way.
"There's an assumption that treating cancer is expensive but it doesn't have to be. For some types it can cost as little as £20 to cure a child.
"By developing treatment regimes that take account of a country's medical facilities and providing proper training and advice to local doctors, we can get money to the countries that need it and begin a co-ordinated programme of communication and training."
Dr John Toy, Cancer Research UK medical director, said countries must work together to tackle the problem.
"In many parts of the world cancer still for many children means an automatic death sentence," he said.
"A proper solution, however, requires a truly international response."