Angelina Jolie has admitted that her kids often ask why she and her partner Brad Pitt aren't married.

The actress has three biological children with Brad and three adopted children.

In the past the pair have said that they refuse to get married until everybody in the United States, including same-sex couples, are allowed to legally tie the knot.

However, Angelina confessed that there is a certain expectation from her family that her and Brad should get hitched.

"They have asked, yeah, because ... people get married in the movies," Angelina told Nightline in an interview that airs on Monday. "Shrek and Fiona are married, you know?"

The star said it a tricky subject to brace with her kids whose ages range from three to ten-years-old.

But she does have an explanation to reassure her brood that she and Brad are completely committed to one another.

"We've explained to them that our commitment, when we decided to start a family, was the greatest commitment you could possibly have," she said

Angelina also jokingly questioned their motives behind a wedding.

The 36-year-old suspected they may just be after the sweet treats.

"I asked them if it was just because they wanted to have a big cake," she laughed.