Elsa, voiced by Idina Menzel, from left, Anna, voiced by Kristen Bell, Kristoff, voiced by Jonathan Groff and Sven in a scene from "Frozen 2." Picture: AP/Disney

"Frozen 2" star Kristen Bell told her children "everything" about the movie after she read the script because she wanted to be a "cool mom", but warned them their teeth would fall out if they told anyone.

The 39-year-old actress has children Lincoln, six, and four-year-old Delta with husband Dax Shepard, and she told them "everything" that was happening in the upcoming movie - in which she voices Anna - because she wanted to be a "cool mom".

She said: "I told my kids everything. I was in the mood to be a cool mom. I tell them all the time. I tell them two things.

"Number one: All your teeth are going to fall out, which is the best thing you can say to a kid.

"Number two: I was like, 'OK, here's what happens.' After I read the script, I told them everything.

"They were excited and then it occurred to me that I was in breach of my contract.

"I'm thankful now that it's out that I can no longer get sued by Disney.

"I said to them it was very important that they don't tell anyone at school."

But Kristen - who stars alongside Idina Menzel (Elsa) in the motion picture - admits it was a "mistake" to give her kids the 'Frozen 2' spoilers.

Speaking on SiriusXM, she added: "It was a mistake. The teeth thing I stand by."

The hotly-anticipated sequel is released later this month, six years after the original hit the big screen, and Kristen believes there was such a long delay because Disney wanted the story to be right.

She said: "The reason they didn't green light it so quickly is because nobody knew what it was gonna be.

"Nobody wanted it to be episode two of 'Frozen', where Anna lost her shoes. No. It was about, 'What are the emotional undercurrents where we can show growth and character development in these people?'

"It's not just about providing a problem and having an end of a second act, and then a third act. It's a beautiful story, and I think it says something pretty powerful.

"I'm glad that they took the time that they did because I think it's really good. And it's definitely a different 'Frozen'. It's a more developed 'Frozen'."