Gwen Stefani Shows Off Baby Zuma!

By Eunice Oh

10/30/2008 at 04:00 PM EDT

Two months after giving birth, Gwen Stefani is showing off her newest bundle of joy: Zuma Nesta Rock Rossdale.

The singer, who was spotted with the newborn at a Beverly Hills library on Wednesday, posed with son Zuma in a photo taken by her father, Dennis, and posted on No Doubt's Web site.

"Gwen, Gavin, Kingston and Zuma are all doing well and enjoying being a party of four," reads a message accompanying the photo.

Dad Gavin Rossdale recently told PEOPLE that juggling two sons with wife Stefani hasn't been too challenging.

"One is one, and two is 10. That's all we know," he joked. "[But] it's not so bad. We've got it down now, you know."

Older brother Kingston, however, is having a tougher time.

"It's like, here is this guy, and he's not leaving. [Kingston] is getting used to that," Rossdale said. "Obviously, there are moments that he's bugged out that someone is in his spot with his mom."