Jennifer Garner had quite the bash for her 38th birthday party on Saturday afternoon! “Jen wanted everyone to feel like they could bring their kids, so she didn’t want to have it at night,” a party-goer told RadarOnline.com . Among the guests was her “Juno” co-star Jason Bateman, with his 3-year-old daughter, Francesca; actress Reese Witherspoon; actor Tobey Maguire with his wife, Jennifer, and their 3-year-old daughter Ruby; and model Molly Sims . “Even though there were a bunch of celebs there, it didn’t feel like a Hollywood party at all,” the spy told the Web site. “It just seemed like some friends getting together to celebrate a birthday.”