The Christian charity says conflicts and flooding are creating severe food shortages in the country, and the UN has warned that 50,000 children in South Sudan could die by 2015.
The program director for World Vision's work in South Sudan, Perry Mansfield, said: "When we get distracted by language and trying to define a problem in abstract percentages we can forget that every night more people than the population of the city of Los Angeles go to sleep hungry."
"Among them are children, pregnant women and the elderly, and it's tempting to think everything will be fine because we haven't reached famine conditions, but these people are in crisis and if we act early and act fast we can save lives."
The United Nation's report says humanitarian aid from organisations is helping to ensure South Sudan doesn't enter a period of famine.
A country is officially experiencing famine when one in five homes face extreme food shortages with little ability to cope.
South Sudan is the world's youngest country, having officially declared independence from the Republic of Sudan in 2011.