The actress, who has daughter Apple, 8, and son Moses, 6, with Coldplay frontman Chris Martin, explained it is beneficial for her kids to be in dirt and germs to build up their immune systems.
Talking to OK! magazine, she said: "When they get home from school, I ask them to wash their hands but I think it's good for them to be in dirt and germs because that's how you build an immune system - by getting sick.
"I mean, if someone has the flu, I don't put my kid in their face, but it's an inevitable fact of life."
The 39-year-old also said that she used to follow a macrobiotic diet but has now swapped that for more variety.
She added: "I'm not vegetarian, I don't eat red meat, I haven't eaten red meat in a long time, but I eat fish and birds. I drink, I smoke once in a while - when in Rome, you know what I mean?
"I don't count calories, but that's because I exercise like a fiend. You can't have one without the other."