Barrymore, 33, a WFP ambassador against hunger, announced her pledge on The Oprah Winfrey Show to kick off the agency's $3 billion "Fill the Cup" campaign that aims to feed 59 million hungry school children in developing countries for a year.
WFP hopes the United States will be able to donate enough money to feed 10 million of those children.
"I have seen with my own eyes what a difference a simple cup of nutritious porridge can make in a child's life," said the Charlie's Angels star, who has travelled to Kenya twice in the past two years for WFP.
"It helps them learn, stay healthy and sets them on track for a bright future. I urge everyone - everywhere - to help WFP 'Fill the Cup' for hungry children, and make hunger history," she said in a statement released by the agency.
Barrymore, who gained fame as a child star in the film ET: The Extra-Terrestrial, is the eighth-highest-paid actress in Hollywood, according to The Hollywood Reporter, earning more than $10 million a movie.
The WFP is facing a $500 million gap in funding this year due to the rising cost of food - up 40 per cent since June, WFP officials said. That prompted the actress to visit the world's largest grain trading floor in the Chicago Board of Trade building on Monday where corn, wheat, soybean and rice futures trade.
Josette Sheeran, WFP's executive director, said $50 "fills a child's cup for a year" and called on people to donate through the Web site www.wfp.org.
"They feed their families with it ... they get an education so therefore you're changing the future," Barrymore said after touring the floor, including a trip into the corn futures pit.
The organization said last year it provided more than 20 million school children with a daily cup of porridge, rice or beans and also gave many girls a monthly ration to take home to their families. It said up to 70 per cent of its food used for school meals is bought from farmers in developing countries.
