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.

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.

• Gwen Stefani, taking son Kingston, 23 months, to

a sing-along version of Disney’s The Little Mermaid at the El

Capitan Theater in Hollywood. Hubby Gavin Rossdale also got in on the

musical fun - and the family left the theater with a DVD, an onlooker tells us. (More “Under the Sea” fun at home?) First, though, the family stopped by Coldwater Canyon Park, where Kingston ran around and enjoyed the playground.

• A naturally made up Victoria Beckham, happily

shopping at the boutiques along Santa Monica’s Montana Avenue. Wearing her

trademark skinny jeans and high heels, Posh had a shopping companion in son

Brooklyn, 9. (The mother-son pair was joined by a bodyguard, too.) As for

her stops, Beckham visited lingerie stores Lisa Norman and Pink Lili. She

also did some window-shopping at Kovan Jewelers before taking off in a

waiting white Lexus SUV.

• On a break from promoting Iron Man, Gwyneth Paltrow headed down to Paris’s Place Vendome, detouring into

jeweler Fred before joining friends for a quick lunch across the street at

Hotel Costes.

• Also in Paris: Paltrow’s costar Robert Downey Jr. and wife

Susan Levin, strolling the Tuileries Garden and stopping in at the

Musée de l’Orangerie to see Monet’s “Waterlilies.” Afterward, they

lunched at Montparnasse’s celebrated Closerie des Lilas before another walk

- this time in the Luxembourg Gardens.

• Avril Lavigne, getting friendly with Alli Sims - yep, Britney’s “cousin”

- over dinner at STK in New York.

• Entourage’s Adrian Grenier, lunching on the

outdoor patio at the Waffle in Hollywood. He was dining and laughing with a

buddy, but also spent a good amount of time texting on his cell phone.

• By PERNILLA CEDENHEIM, MARK DAGOSTINO, JENNIFER GARCIA, LISA

INGRASSIA and PETER MIKELBANK

Celebrity Hot Spots.

Monday’s Couples Watch >

Don’t expect Gwen Stefani and Gavin Rossdale to be stocking up on baby items in pink or blue just yet. The couple, who are expecting their second child, will find out if they’re getting a boy or a girl on delivery day, Rossdale said Wednesday.

“We don’t know %26#91;the baby’s gender%26#93;. It was a surprise last time so we’re kind of working on that this time,” he told Ryan Seacrest on his KIIS-FM radio show. “There are some %26#91;names%26#93; floating around the house, bouncing around the walls.”

The big brother-to-be, who turns 2 next month, has also been entertaining his parents with his growing vocabulary. “He speaks now,” said Rossdale. “It’s pretty cute. He’s got a funny way of saying things and a funny voice. He’s pretty vocal.”

Stefani, 38, has described her son as a “chilled-out little guy … he’s super-cute and super-entertaining.”