The 'Mirror, Mirror' actress has had to "tone down" her antics because she was enjoying shocking twins Hazel and Phinnaeus, seven, and four-year-old Henry - her kids with husband Danny Moder - more than she felt she should.

She told TV talk show host Ellen DeGeneres: "I realised I was getting too much joy out of it so I've had to tone it down... Just like if I hear them coming and they don't know where I am in the house. I crouch down in there private space and they come in and just jump out.

"Little people can just catch air. They just vault. It's so wrong."

However, Julia herself proved easy to scare when Ellen jumped out on her as she left her dressing room.

The actress explained: "Oh my God! Am I the perfect person to scare or what?"

She later added on the show - which airs in the US today (23.03.12) - "It doesn't even come across how scared I was - it did not come across there and I changed [outfits] because I peed in my pants! I screamed like I was being mugged on a subway."

Later in the interview, the actress was shocked again when a man dressed as Snow White - the central character in hew new movie 'Mirror, Mirror' - sneaked up on her, causing her to scream loudly.

She then laughed and said: "Thank God, I'm a jogger - I would have a heart attack. Who was it? That's a different Snow White!"