A two-time Academy Award nominee, Ruffalo will have an onstage conversation with the festival's young jurors, said the Hollywood Reporter.
The Giffoni jury consists of thousands of kids from 52 countries, who will judge films according to their age group.
Films in competition include Carol Morley's "The Falling, starring Game of Thrones' Maisie Williams, and Lou Howe's debut "Gabriel". The final lineup will be announced in June during the Milan EXPO.
The festival is described as a sounding board for cinema for young people. It has launched outposts in several countries over the years, including one in Georgia in October. Alan Rickman, Jessica Alba, Meryl Streep and Nicolas Cage have attended in recent years.
The 45th edition of the Giffoni Film Festival runs from July 17-26.