On Monday – only two days shy of a month after giving birth to her second child – Naomi Watts was close to having back her pre-baby figure, as evidenced at the Cinema Society and Nextbook.org-sponsored New York premiere of her partner Liev Schreiber’s World War II drama Defiance.

How did she manage to drop the baby weight so quickly? “I’m breast feeding,” Watts, 40, told PEOPLE about her routine with Samuel Kai Schreiber. “And he’s sucking it all out of me, it seems. And when the baby comes out, it’s a lot of weight right there.”

A couple since 2005, Watts, 40, and Schreiber, 41, also have another son, Alexander Pete Schreiber, born in July 2007.

“They’re very different,” Watts said of her two boys. “[Sammy]‘s more fragile, in a way. But I don’t know, maybe I’ve forgotten how small they are. [Alexander] is only 18 months old.

“And I’ve also got this big baby right here,” she said, pointing to Schreiber at her side on the red carpet.

Splash, Source