{blackbabes} Nicole Richie Throws Sparrow's First Birthday Party

Nicole Richie Throws Sparrow's First Birthday Party | Nicole Richie

Nicole Richie may have parted from her past party girl ways, but she can still throw a good bash – especially if she's celebrating her son's first birthday.

Richie, along with fiancé Joel Madden and big sis Harlow, 2 ½, held a party for Sparrow Saturday. He turns 1 on Sept. 9.

About 50 guests, including actress Ellen Pompeo and her daughter Stella Luna, 11 months, and Sparrow's uncle Benji Madden, gathered in the backyard of the family's Hollywood Hills home and noshed on birthday cake. The backyard was decorated with red, green, orange and purple "Happy Birthday" balloons for the occasion.

"Nicole was keeping the party simple to not overwhelm Sparrow," a source at the party tells PEOPLE. "Everyone seemed to have a great time."