According to the Los Angeles Times,
Seth Green spent six weeks in a special sensor-equipped performance-capture suit while performing his lines as Milo. During post-production, the filmmakers noticed that Green was able to physically imitate the movements and behaviors of a 9-year-old boy, but his voice sounded too mature for the character. His voice was replaced by that of 11-year-old
Seth Dusky. Green's voice still appears as the voice of one of the hippies on the '70s television show Ki watches. The first trailer, which was published on November 22, 2010, features Green's voice for Milo intact, implying that Dusky replaced the dialogue very shortly after this trailer was released.
