(Cover) - EN Movies - Judd Apatow was happy to cast his daughters in upcoming comedy This Is 40.

The writer-and-director of the Knocked Up sequel hired his two children to portray bickering siblings in the feature. Judd is father to Maude, 14, and Iris, eight.

This Is 40 highlights what life is like for Knocked Up characters Pete and Debbie a few years following the circumstances of the first film.

Judd was impressed by his daughters’ acting ability.

"They're not scared that cameras are around," he told The Hollywood Reporter.

"They get sucked into what their real problems are with each other. Like, they're so annoyed with each other that they're not distracted by the fact that they're shooting a movie and it needs to go well, they're more concerned about whatever argument I'm trying to make them have on camera.

"So if I say, 'OK, Maude, tell her she can't watch Lost, she's too young,' Maude wants her to not watch Lost. She's mad. She's like, 'I'm 14-years-old, I'm allowed to watch Lost, and you're eight, you have to wait six years, and if you see it before six years, I got screwed.’ And so she's mad, and Iris really doesn't get why she can't watch Lost… and then they just get sucked in, and they forget [they're filming]."

This Is 40 will be released in December.