Anna Faris is "fascinated" by her son.

Anna Faris

Anna Faris

The 40-year-old actress has four-year-old son Jack with her husband and 'Guardians of the Galaxy' star Chris Pratt, and has said the most "rewarding" thing about being a parent is being able to watch her son "become a person".

She said: "It's just so fascinating watching him become a person. It's so rewarding."

But the 'Scary Movie' actress finds disciplining Jack difficult, as he's inherited his parents' sense of humour and she can't help but laugh at him.

She added: "I try [to discipline him] but I can't help but laugh. He'll be like, 'Mom, I have cheese foot! My foot smells like cheese!' He's so funny!"

Although Jack is still young, Anna says he's starting to figure out what his famous parents do for a living, especially when he sees billboards of 38-year-old Chris.

Speaking to People magazine, Anna said: "He's definitely coming around [to understanding our jobs]. We'll drive past a billboard of Chris for 'Guardians of the Galaxy' and Jack will be like, 'Hey, Dad!'"

Meanwhile Anna recently opened up about her fear when she took her son to the premiere of 'The Emoji Movie', as she was anxious about the scale of the event.

She said: "I guess he loves attention just like mommy. But it does feel like, 'Am I doing the right thing as a parent?' It's also terrifying to bring your kid to such a public event."

Chris, however, previously said having his son with him on a recent promotional tour helped bring him "back down to Earth".

He said: "That has been the best part of this world tour by far. It's nice to have your family with you because it brings you down to earth and when you leave your feet on the ground, you realise what it feels like to have your head in the clouds.

"You go with the flow and things come and go and you're not even there to record or observe them. So when your family bring you back down to earth you get to experience this - or at least I do - in a while different way. When they are present with me, I get to be present with me as well."