The `Larry Crowne` actress - who has seven-year-old twins Hazel and Phinnaeus and four-year-old son Henry with husband Danny Moder - has taken up some new hobbies so that her "brain doesn`t turn to mush" as she gets older.
She said: "I`ve startedsewingclasses recently. I made some big pillows for the kids and some really simple pants for Danny. I`m also taking piano lessons with my kids.
"In your 40s, you`re supposed to learn new things so your brain doesn`t turn to mush. So now I`m practising piano scales."
Julia did not used to "appreciate" the spare time she had earlier in her career, and she now spends a lot of free time with her family.
She added: "I must have had bags of spare time before I had children but I don`t know what I did with it and I didn`t appreciate it. But it`s such a terrific trade off."
The 43-year-old beauty recently described Danny - who she wed in 2002 - as her "best friend", and believes it was her destiny to marry him.
She said: "I hope there are good people who agree that I have done good, kind things in my life. But to really, ultimately, stand fully in a moment of realising that I was born to love and be the wife of this man.
"Danny is my best friend, my truth-teller. There`s something you can build a life on.
"He stands by the choices he has made. He will never blame it on somebody else and I have never seen anybody else do that."