Also read: Kate Hudson Wants 'Something Borrowed'
Hawn let the news slip in an interview with the London Evening Standard's ES magazine.
"My kids are fantastic with their children, they have an amazing parental ethic and I'm very proud of them for that," Hawn, 66, said.
"When my daughter Kate married an English rock star [Matt Bellamy] it didn't worry me; all that matters is that the relationship is a good one. What people do is not necessarily who they are," she continued.
The 32-year-old actress and Bellamy announced their engagement in April 2011 and they welcomed their son, Bing, last July.
Hudson was previously married to Black Crowes frontman Chris Robinson from 2000 to 2007. They have an eight-year-old son, Ryder.