KEVIN COSTNER is starring in the indie comedy 'Swing Vote,' and ET's own MARY HART -- who has a cameo in the movie -- is with the veteran actor on the set in the sleepy town of Belen, New Mexico!

The political satire positions the Oscar-winning star as a single father and loveable loser who is unwittingly placed in the national spotlight when the presidential election comes down to his vote. The film is scheduled to come out next summer before the big real-life election.

"This is a very Americana movie," says Kevin. "'Swing Vote' is filled with those kind of moments that you didn't see coming."

As for the coming 2008 election, Kevin won't reveal his hand, saying, "I think voting's a private thing," but offers his opinion: "I think it's really important that these candidates start raising the stakes for us, not for themselves; they need to quit playing it really safe."

Kevin and his wife CHRISTINE also welcomed a baby boy this past May, their first child together. CAYDEN WYATT COSTNER is the fifth child for the 52-year-old Kevin, and the first for Christine; the couple married in 2004.

"I love [my kids] and it's an everyday thing -- you've got to be an active participant," shares Kevin. "[Cayden's] a world traveler. I think a lot of people who grow up in the movies already have more stamps on your passport than you can imagine. [He's] been around already."

Watch ET for more with Mary and Kevin!