Kidman portrays the actress-turned-royal Grace Kelly in the upcoming film Grace of Monaco.
Kelly's children, Albert, and princesses Caroline and Stephanie, have disapproved of the project, saying it's based on "erroneous and dubious historical references."
"I know they're upset. I would be, too, if it were my mother," Kidman told Britain's Daily Mail.
"It's a child's job to protect their parent,' she added. "In that regard, I get it. I get why the children are upset.
"I can't say much other than that I have great respect and regard for their mother."
Kidman said the movie isn't meant to serve as a biography of Kelly.
"It's not meant to be a biopic. I certainly did my best to honor everything that was real and truthful in it," she said.
The film opens Wednesday at the Cannes Film Festival.
Take a look at the trailer: