Kristen Bell and Dax Shepard have been forced to explain swearing to their children.

The couple have two daughters - Lincoln, six, and Delta, five - together, and after one of their tots asked what it means to raise a middle finger to someone, they've had to explain the concept of swear words and gestures to their brood.

In a series of videos shared to her Instagram Story, 'Frozen' star Kristen can been seen trying to hold back laughter as Dax attempts to explain the concept to his daughters off camera.

One daughter says in the clip: ''He says this is 'f**k'. He says that every time in school. The teacher says that's a bad word.''

And Dax, 44, replies: ''He does? He's naughty. Yeah, that's not a nice word. You know, that's a naughty finger and I never see you do that. It makes me so proud that you know that, yet you don't do it. Well, you did it a couple of times when you were young, before you knew it was a naughty word.''

Kristen explained in a caption on the clips that she has been ''waiting for this conversation'' ever since she fell pregnant with her first child.

She wrote: ''I have been waiting for this conversation since the day i got pregnant.

''The one where we talk about what fingers mean what when u hold em up.

''I fidgeting because i am trying so hard not to laugh. Its excruciating. @daxshepard, u handled this brilliantly. (sic)''

Meanwhile, the 39-year-old actress recently praised her spouse for mastering ''acts of service'' that help to keep their romance strong.

She said: ''My husband literally said to me this morning - I mean, were 13 years in but he's gotten it now - he woke up 10 minutes after I did and I was scrambling to get out of the house and he said as he was like, rising out of bed, he said, 'Is there anything I can help you do to help you get out of the house on time?' And I was like, 'Are you trying to make me horny right now? What are you doing?'

''Acts of service to other people are also very sexy, but if you pour your coffee and hand me a mug as well, I'm there.''