It was a who’s who of celebrities – and their babies – at Kingston Rossdale’s second birthday party.

Gwen Stefani and Gavin Rossdale threw their son an animal-themed bash at their Studio City, Calif., house on Sunday – one day before his actual birthday. The fete drew 40 friends, including Nicole Richie, Joel Madden and daughter Harlow, as well as Victoria Beckham and son Cruz, and Christina Aguilera, husband Jordan Bratman and son Max.

The family’s backyard was outfitted with small safari animals and multicolored balloons. There was also a pony for the children to ride. And a big moon bouncer kept everyone – adults and their kids – entertained.

At one point, Rossdale and the birthday boy joined several of the younger guests in the moon bouncer, while a pregnant Stefani bonded with Richie’s daughter, an eyewitness says.

Victoria Beckham seemed to enjoy the party as well, kicking off her heels to play with her son, who sported a monkey costume. “She took her shoes off and walked around the backyard with bare feet,” the eyewitness reports, noting that Cruz especially loved the pony, riding it around the backyard several times.

The following day, Stefani and her husband celebrated their son’s birthday again – with a little quality time on a Malibu beach.