Talk to Julia Roberts about motherhood, and she's bound to gush. "I definitely feel that I've expanded as a human being," she recently told Oprah Winfrey about raising 2-year-old twins Hazel and Finn (short for Phinnaeus) with her husband of 4½ years, cameraman Danny Moder. "I feel so blessed on a level that I can't even wrap my mind around."

And now, another blessing: On Dec. 29, the Oscar winner confirmed to PEOPLE that she's expecting a third child—just one this time!—this summer. The news kicks off another year in which Roberts is likely to focus on family: Talking to Winfrey about spending time with the twins, she said, "I felt like I had worked for 18 years at my career, and this [is] my reward that I got to stay home with my children."

When Roberts has chosen to work, she has made sure to bring along the brood: She recorded her animated role for Charlotte's Web in a studio near her Taos, N.Mex., ranch, relocated her family to New York City while she acted in the Broadway play Three Days of Rain, and in October celebrated her 39th birthday with the kids and Moder, 37, in Morocco, where she shot the upcoming drama Charlie Wilson's War. Looking ahead to her next big birthday, she told Diane Sawyer last month, "I really am [looking forward to turning 40] because I just have the best family. And so the idea of getting older just, to me, is having more adventures with them." Along with, of course, the new little adventurer on the way.