Naomi Watts
Eamonn McCormack/WireImage
"You drop some weight just by running after them," she tells PEOPLE.
Watts, 40, most recently gave birth to son Samuel Kai with boyfriend Liev Schreiber. Their first child, Alexander Pete, was born in July 2007.
The Aussie, who can be seen co-starring with Clive Owen in The International, exercised and walked a lot during her pregnancy. She adds that nursing also helped her drop the weight.
"I was hungry the whole time and I'm still hungry all the time!"
• Reporting by JENNIFER GARCIA
