Celebrity Reese Witherspoon's 33rd Birthday Surprise She is serenaded by co-stars at Monsters vs. Aliens premiere By Scott Huver Published on March 23, 2009 01:25 PM Share Tweet Pin Email Photo: Carolyn Kaster/AP Reese Witherspoon had to work on her 33rd birthday on Sunday – but she got a star-studded surprise all the same. Witherspoon arrived the Los Angeles premiere of Monsters vs. Aliens – in a shimmering, super-short dress by Rodarte – and had just made her way into the Gibson Amphitheater when she and her co-stars were called to the stage by DreamWorks studio head Jeffrey Katzenberg. After Seth Rogen, Kiefer Sutherland, Rainn Wilson, Paul Rudd, Hugh Laurie, Will Arnett and Amy Poehler gathered onstage with Witherspoon, Wilson announced that the group was about to stage an “intervention” for the Oscar-winning actress. “We have some hard facts to run by you, because we know it takes a full bottle of Nyquil for you to fall asleep at night,” Wilson told Witherspoon, “so there’s something very special that we want to say.” Cake and Candles He and his fellow actors then launched into a rendition of “Happy Birthday,” joined by the theater audience, as a cake was wheeled onto the stage. Amy Poehler punched home the final verse, singing “Happy birthday, Reese WITHERSPOON, Happy birthday to you!” “Thank you for coming to my birthday party – I mean, the screening of Monsters Vs. Aliens,” the slightly taken-aback Witherspoon told the crowd. Witherspoon told reporters while promoting the film two days earlier that she was looking forward to the birthday. “It is a great thing to be able to be doing things with my kids and having them be proud of me. What’s better than feeling like you’ve accomplished things in life?” Monsters Madness at Home Witherpoon said that her new film in particular has increased her cachet with her kids – daughter Ava, 9, and son Deacon, 5. “My kids managed to maintain their coolness for a while, but literally it has hit fever pitch at my house. They are rabid and they wake up in the morning [asking], “When can we watch this movie?” Witherspoon said she shares certain qualities with her character in the 3D animated movie, Ginormica, an unlucky bride-turned-monster who towers over everybody around her. “Tenacity, fierceness, taking care of the group,” she said. “I’m kind of a mother hen that way, even on movie sets. But at 5’2”, she doesn’t think she’ll ever quite relate to the character’s giant stature. “I think I actually shrink [as I get older],” she laughed. “My mother is now four feet tall.” RELATED GALLERY:• 2003: Reese dishes on expecting baby no. 2RELATED GAME:• Flip & match Reese’s movie roles in Concentration!