updated 01/09/2011 AT 3:00 PM ET
•originally published 01/09/2011 AT 1:00 PM ET
Happy birthday Harlow Madden!
The afternoon birthday bash took place Saturday at the Treehouse Social Club in Beverly Hills, a full-time play center, café and pampering spa for moms and their kids.
Guests included Harlow’s 16-month-old brother Sparrow, actress Ellen Pompeo and Chris Ivery with their daughter Stella, 15 months, Jessica Alba and Cash Warren with their daughter Honor, 2½, Gwen Stefani and Gavin Rossdale with sons Kingston, 4½, and Zuma, 2, Kourtney Kardashian and son Mason, 1, Jennifer Meyer Maguire with children Ruby, 4, and Otis, 20 months, and Sara Gilbert with daughter Sawyer, 3.
“It was a fun, casual party. Besides the celebrity kids, Harlow had a few friends from school at the party and she was very excited. The kids played outside in the Treehouse and enjoyed art and crafts projects inside. All the moms chatted while the dads bonded and it was a perfect party for both the adults and the kids,” a source tells PEOPLE.
Guests snacked on healthy food, including sandwiches and Harlow was also presented with a special birthday cake.
“Nicole looked great and had fun at the party. She and Joel definitely looked like happy newlyweds,” adds the source.