Cameron Diaz taught her 13-year-old co-star to swear.

The ‘My Sister’s Keeper’ actress decided it was time Abigail Breslin – who plays her daughter in the new movie – knew some bad words, so decided to widen her vocabulary.

Cameron explained: “I did teach Abby how to say the f-word. I taught her how to drop the f-bomb in every way possible.

“I said, ‘You’re a child in an adult’s world. I can’t be a child for you.’ When she didn’t swear, I said, ‘You’re starting to offend me, Abby. If you don’t start swearing every three words then I will fine you.’

“I even told her mother that I was teaching her to swear and she said, ‘It’s about time.’ ”

Cameron plays Sara Fitzgerald, whose daughter Kate – played by Sofia Vassilieva – has terminal cancer.

Abigail stars as Sara’s other daughter Anna, who was a designer baby born to help keep Kate alive.

During the film, Anna decides she wants the right to make her own medical decisions.

Cameron’s father Emilio Diaz died after developing pneumonia while she was working on the film, and she claims starring in the movie helped her deal with her grief.

She added to the Chicago Sun Times newspaper: “Being able to go back to this group of people was a blessing. Literally these girls in my new movie helped me.

“We’re not living or dying. We’re not happy or sad. It’s all happening at the same time. Sometimes when you’re at your happiest, you’re also at your saddest.

“Life is bittersweet. You can be celebrating and having the best day of your life and someone is dying.”