The actress plays a hippie mum in the Sam Mendes. film - her first project since becoming a mother in October 2006.
And when her tiny co-stars threatened to ruin filming by screaming through take after take, she decided to try to calm them.
She explains, "I get to working with a five year old and two 11-month-old twins, who screamed through the entire day.
"If I had not been a mom and known how to calm a baby, talk and hold the baby, the whole day would've been wasted.
"I thought, 'Thank God I'm a mother.' But I didn't feel like I've gone to work and expressed myself and now I'm ready to go home to my baby. I felt like I was a mother all day on that movie.
Source: WENN