Milo's (Seth Green) mom (Joan Cusack) is wearing a Carolina Panthers jersey with the name Smith and the number 21 on it when she is taken to Mars. As of the 2011 season no player with the last name Smith has worn 21 in the team's history. (Most recently the number has been worn by defensive back Brandon Hogan.) Because of this, Smith may be Milo's family's last name, as fan apparel is often customized in this manner.
This movie grossed $6.8 million in its opening weekend, which is the 19th-worst opening ever for a film playing in more than 3,000 theaters, and one of the worst openings for a major 3D release. With a budget of $150 million and a total gross of just $39 million, this movie is considered a massive box office bomb, and has the worst-ever financial reputation for a film branded by Disney. Its commercial failure contributed to Disney canceling its planned remake of Yellow Submarine (1968), which was to be made with the same motion capture technology.
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 Robert Dusky. Green's voice still appears as the voice of one of the hippies on the '70s television show Ki watches. Mars Needs Moms Trailer 1, available on the Internet, was made with Seth Green voicing Milo.
The makers came up with their own alien language. Elisabeth Harnois stated in an interview that she and the cast were given scenarios by Wells to which they acted out responses in improvised Martian language.