From PEOPLE Magazine Click to enlarge
It was a sunny spring Saturday afternoon in Los Angeles, perfect for the birthday party of a little A-lister. At Heidi Klum's hillside Brentwood mansion, the festive decor featured a doll pinata as Klum's oldest daughter, Leni, celebrated her 8th birthday along with her siblings Henry, 6, Johan, 5, and Lou, 2-and their little buddy Louis Bardo Bullock, 2. For Klum and Louis's mom, Sandra Bullock, it was a chance to catch up. "Sandra and Heidi hugged and looked very excited to see each other," says a party guest. "Louis was happy and excited about all the toys. They stayed for hours."

Just another day in the life of Hollywood's most glamorous single mom—and the most important guy in her life. Since splitting from ex-husband Jesse James in 2010, the Oscar winner, 47, has been on her own with little Louis, while the whole world has watched him grow from a cherubic baby to a fun-loving, likes-to-paint-and-get-his-hands-dirty 2-year-old. "Being a mom is her total focus now," says a Bullock source. Along with her work, "Louis has become her whole life."

For Bullock, going it alone as a mom wasn't the dream she signed up for, but it is one she's embraced. "Sandy seems very happy, but it's hard," says another Bullock source. "She's raising Louis as a single mom, and she never thought it would be this way. She's still trying to figure out [her new life]." She's thrown herself into giving Louis the most regular-kid life he can have given her celebrity. From shuttling him to preschool to setting up playdates and special outings, she's "very hands-on," says a source. "She is giving him the best, most normal life she can."

Having wrapped the outer-space drama Gravity with George Clooney (due out in November), she's been settling into life in L.A., where Louis goes to preschool. Bullock has been renovating a $16 million, 8,100-sq.-ft. Beverly Hills mansion that she bought last year to serve as a permanent nest. "Sandra is putting a lot of money into the house to make it comfortable and safe for her son," says a source. Working at her Fortis Films production office, she squeezes in meetings and workouts with a nearby private trainer before Louis gets out of school. "Louis is a really outgoing, funny little kid," says a Bullock source.

And he's got the passions of a typical 2-year-old. In April Bullock took Louis to see a full-size version of Thomas the Tank Engine in Fillmore, Calif. On their train ride, "Sandra looked as excited as Louis," says an observer. He's good company on adult errands too: On a recent outing at the antique store Material Environment in L.A., she selected vintage chairs while Louis explored. "Sandra acted like a great mom," says an observer. "Her boy was very sweet, happy and well-behaved."

But even the most devoted mom needs a little me time. For Bullock, that means hanging out with a trusted circle of pals and slipping out for the odd grown-ups' night out. Last fall she was spotted dancing at a friend's birthday party at Beacher's Madhouse at the Hollywood Roosevelt Hotel, and on March 16 she hit Mr. Chow in Beverly Hills with a group that included Klum (see box). "They were toasting and giggling," says an observer. Adds another: "It was cute to see Sandra and Heidi so happy."

As for romance, Bullock would like to find someone she could get serious about, says a source. But she's doing just fine on her own: "Louis has grounded Sandy and helped her focus on other things." Bullock's fondness for her close male friends-best buddy Jonathon Komack Martin is producing partners with another old pal, Ryan Reynolds-sometimes sparks romance rumors, but the relationships are strictly platonic. As much as the world may want to see America's sweetheart happy and in love, it's not something that Bullock is going to rush into, says a source. "She is going to be very careful about who she allows in her life because of Louis," says the source. "He is her priority. He is her world."

  • Contributors:
  • Elizabeth Leonard/Los Angeles,
  • Pernila Cedenheim/Los Angeles.