The actress reveals her dad, filmmaker Ron Howard, kickstarted the trend of allowing his kids appear in his movies when they turned seven - and she has adopted it for her children.

She says, "I was in Parenthood and my son turned seven during this movie, so he got to be in the movie as an extra and he's in a petting zoo scene and he hugs a dinosaur. There was a guy with kind of a sock puppet... and he hugged the arm. He was pretty good."

Young Theo also landed an extra spot in mum's follow-up movie, Pete's Dragon.

Howard admits the family tradition extends to her mum, who reluctantly appears in all her father's films.

She explains, "My mom and dad were 16 years old when they got together and so by default, when he was making movies with his Super 8 camera in high school, he would ask her if she could be in it. She's not an actress and feels really uncomfortable in front of the camera, but she would always say yes and help him out.

"He's superstitious and now he can't do a movie without my mom being in the background."