All of the girls acting as participants in the "Little Miss Sunshine" beauty pageant, except Abigail Breslin, were veterans of real beauty pageants. They wore the same costumes, including hair and makeup, and performed the same talent routines as they had in their real-life pageants.
Steve Carell, at the time he was cast for Little Miss Sunshine (2006), was a relative unknown in Hollywood. According to an article in Entertainment Weekly, the producers of the film worried that he wasn't a big enough star and didn't have much acting experience. However, between the time the film was shot in the summer of 2005 and its release in the summer of 2006, Carell became a huge success as the star of the high-grossing film The 40-Year-Old Virgin (2005) in August 2005 and the leading character of the popular NBC Emmy-winning television series The Office (2005), which premiered in March 2005 and for which Carell won a Golden Globe in 2006 for best lead actor in a comedy television series. In the span of just one year, Carell had become such a star that the producers had gone from protesting his casting to tapping him to do prominent promotion for the film.
While filming in a convenience store in Santa Clarita, CA a Paul Dano look-a-like walked in. Dano was late and unaccounted for so everyone thought the look-a-like was Dano. After he explained that he was not Dano, they took some pictures and sent him on his way.
The film was dedicated to Rebecca Annitto, the 14-year-old niece of producer Peter Saraf, who was killed in a traffic accident in 2005. She appeared as an extra in scenes at Pann's Restaurant and the convenience store.
Dwayne is actually from a previous marriage of Sheryl's. She says toward the beginning "he visited his dad in Florida", and a wedding photo is shown with him in it, but much younger. Olive however is not, because her last name is Hoover, the same as her father's.
On July 25, 2006 Fox Searchlight Pictures invited VW bus owners to a screening of Little Miss Sunshine (2006) at Vineland Drive-In theater in City of Industry, California. 65 VW buses were present at the event.
The trivia items below may give away important plot points.
In the commentary, the directors note that Greg Kinnear was really self-conscious about dancing because his wife made fun of his dance moves at their wedding. He was so self-conscious that he requested the dance scene be eliminated from the film.
When the VW bus gets stuck with clutch failure, the mechanic explains that you don't need the clutch to go from third to fourth gear, but not in the other gear changes. That is not true, with a full syncromesh transmission you can shift every gear using "double clutch" procedure. So you don't need to start in third gear, but eventually a start in first gear was not fast enough from the movie point of view