Gwen Stefani spent $15,000 on her son's birthday party.

The 'Rich Girl' singer and her husband Gavin Rossdale celebrated their son Kingston's fourth birthday on May 26 at their home in Los Angeles, with an extravagant bash which included over 100 guests - including actress Kate Beckinsale and David and Victoria Beckham.

According to UsMagazine.com, the party included a hired a bouncy castle, three birds, a face painter, a balloon artist, and roaming super hero characters, as well as a cotton candy machine and a lemonade stand.

The famous couple - who are also parents to 22-month-old Zuma - recently admitted they hope to add a daughter to their family one day.

Gwen recently said: "Having two boys - there's a lot of energy. I mean, it does seem weird that I don't have a girl, I feel like I'm running out of time."

Although the No Doubt front woman would love a baby girl, she admits that she has no immediate plans to get pregnant again.

She said: "I don't want to spread myself so thin that I can't be good for them. I'm not focusing on it right now, but it's not up to me anyway, you know? These things are miracles, so we'll see."