"My fame, my success that I had on the field, opens doors for exactly things like this - the protection of children, the protection of women," the 39-year-old told reporters at a presentation in London.
"My life has never been just about the football," said Beckham, who has been a goodwill ambassador for UNICEF for the past 10 years and has four children with his wife Victoria, a former pop star and fashion designer.
The fund is aimed at children living in warzones.
UNICEF estimates that one in 10 children in the world - around 230 million - live in such states.
Beckham said his children were "excited" about the project, which uses the website 7.Org.
"They know exactly what I'm announcing today and what needs to be done," he said.