A UAE-Saudi-led blockade on the port city of Hodeidah - amid Yemen's hot summer months - would likely make it the perfect breeding ground for cholera, the charity said.
Save The Children could become "ground zero for a new outbreak of the highly contagious disease", the charity said in a statement.
"Cholera could spread like wildfire in Yemen, potentially infecting thousands of children and completely overwhelming an already crippled health system," said Save the Children International's CEO Helle Thorning-Schmidt has recently returned from Yemen.
"Many hospitals have been reduced to rubble, and those that are still standing are barely functioning. Doctors have not been paid, pharmacies are understocked, and power cuts happen constantly.""
Food and aid have been used as weapons of war and children are paying the price. They are severely malnourished and don't have access to basic supplies like food, clean drinking water and medicine," she added. "This leaves them extremely vulnerable to diseases like cholera, which many are too weak to fight off.
If people are forced to flee fighting on top of this, many children just won't stand a chance."Cholera causes violent vomiting and diarrhoea with undernourished children the most vulnerable to contract cholera.
"More than 13,000 people are believed to have died in Yemen's war, which intensified in March 2015 when the Saudi-led coalition entered the war.Around 11.3 million children in need of humanitarian assistance, while schools and hospitals have been caught in fighting.
Access to food, fuel, clean water and medical supplies have also been compromised. Nearly 8 million children are now going hungry every day and almost a third of under-fives are acutely malnourished, the charity reported.
They are the most likely to die from the disease, with their immune systems badly compromised by malnutrition.
With a breakdown in basic infrastructure in the Hodeidah and thousands fleeing the city almost 3,000 suspected cases reported in the first week of July.
This is the highest numbers seen in Yemen since the start of the year, and a warning sign that a fresh outbreak of the disease is brewing.
A siege on the city would most likely hit Hodeidah's most vulnerable inhabitants - children and the elderly, the poor and sick - leading to the spread of the disease.Safe, drinkable water was already scarce in Hodeidah, but supplies are now severely deminished since the offensive by the Saudi- and UAE-led coalition on the port began in June.
Last year, Hodeidah saw another outbreak, with nearly 164,000 suspected cases out of more than one million reported across Yemen. More than 2,300 people, many of them children, died in that epidemic, which started in April 2017.
