Videos will air on the BBC, ITV, Channel 4, Channel 5 and Sky in an appeal to get the British public to donate to the crisis, caused by droughts and conflict.
Sir Mo, who spent his early childhood in some of the worst affected areas of Somalia, said he was “completely devastated”, urging people to “act now”.
He said: “As a father of four, it hurts to see children without food and water, but this is a reality being faced by parents in East Africa right now.
“The drought is really bad and there are millions of children at risk of starvation.
“I was born in Somalia and it breaks my heart to hear stories of how families are suffering.”
Money raised by the DEC appeal will help those affected in Somalia, Kenya, Ethiopia and South Sudan, with the Government pledging to match public donations pound for pound, up to £5 million.
Between the four countries around 800,000 children aged between six months and five years need lifesaving treatment for severe acute malnutrition, said the DEC.
Meanwhile, in February the United Nations formally declared a famine in parts of South Sudan, the first time in six years such an announcement has been made.
International Development Secretary Priti Patel said: “Britain has acted without hesitation – UK aid funded food, water and emergency healthcare is being delivered across East Africa right now, but more support is urgently needed to prevent a catastrophe.”
“The international community must now follow Global Britain’s lead to save lives and stop the famine before it becomes a stain on our collective conscience. The world cannot afford to wait.”
DEC chief executive Saleh Saeed said: “We are hearing that families are so desperate for food that they are resorting to eating leaves to survive. This is something no family should have to endure.
“Unless we act now the number of deaths will drastically increase.”
Members of the public can donate to the DEC East Africa Crisis Appeal by texting the word SUPPORT to 70000, visiting www.dec.org.uk, or calling 0370 60 60 610.