Kristen Bell's daughter thought her mother was off to ''do a sex'' when she and her husband Dax Shepard tried to sneak away for a couples hike.

The 'Frozen II' star and her spouse haven't been able to spend much time alone during the coronavirus pandemic as their two daughters - Lincoln, seven, and Delta, five - are home from school.

And after the couple tried to sneak out of the house while Kristen's sister was babysitting, Lincoln accused the pair of running off to have sex.

Kristen recalled: ''We tried to steal away for a hike the other day. My sister was here watching the kids. We masked up and we were like, 'Oh, we'll just walk down the streets. There's a great hike near our house.'

''And on our way out the door my seven year old stood in the door and she held it open. She goes, 'Uh, are you going to do a sex?' ''

The 40-year-old actress admitted she has spoken to her daughters about sex before, but the moment still caught her by surprise.

She added: ''It caught us by surprise. We've talked to her about what sex is, but she's never ... we've never talked about us doing it.''

But Dax, 45, knew exactly what witty response to give, though.

Kristen told Stephen Colbert during an appearance on his 'The Late Show': ''Dax just really quickly said, 'We'd love to, but it's illegal publicly. Bye!' and closed the door.''

In March, Kristen opened up on having the sex talk with her kids, saying there's no ''shame'' in discussing the process with children.

She said at the time: ''I do feel strongly about that ... There is nothing wrong with knowing how the penis works and how the vagina works.

''I just don't understand the American shame in that. In fact, I think it equips them to understand pregnancy way better. The agency they have over their bodies to say, 'Oh yeah, this is how it works ... Daddy has a penis, mommy has a vagina. Here's how it works. And here's the part of daddy's DNA and the part of mommy's DNA that grows you like a seed.'

''And by the way, they're so bored by the second sentence.''