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 traveled 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.

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.

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 percent of its food used for school meals is bought from farmers in developing countries.