Model mom! Julia Roberts takes a day off her acting duties to chaperone son Henry on a school trip to the Natural History Museum

She's one of the biggest stars in Hollywood with roles in iconic films like Pretty Woman and Steel Magnolias.

And Julia Roberts played her favourite role as mother as she toted around her 5-year-old son Henry on a field trip in downtown Los Angeles on Friday.

Julia, the teacher: Julia Roberts gladly stepped into the role of a tour guide as she joined her son Henry on a school field trip to the Los Angeles County Museum Of Natural History in Los Angeles on Friday

The 45-year-old kept her youngest close at hand as they made their way around the Los Angeles County Natural History Museum with several of his classmates.

The Pretty Woman star dressed in all black as she played tour guide, chatting away as the group walked in and out of exhibits around the sprawling Exposition Park campus.

Julia, who is set to appear in the on-screen adaptation of the Broadway play August: Osage County later this year, wore her long honey blonde hair in loose curls around her shoulder.

Not your average mom: Julia opted for a classic all black ensemble for the day at the museum

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She and husband Danny Moder are also parents to 8-year-old twins Phinnaeus and Hazel.

The day out was a rare one for the famously low-key star, who lives between Malibu and her farm in Santa Fe, New Mexico.

She opened up to Oprah about her new life hundreds of miles away from the hustle and bustle of the Hollywood movie industry.

Playing the teacher: The 45-year-old held along to her son and his classmates as she led them through the exhibits

Not so fast: Julia kept a firm grip as her son tried to make a dash

'It's peaceful, and it's a relief,' she said of her secluded ranch.

'I always say you can't be in a bad mood here. I don't know if it's New Mexico or just the mountains, but you can't be silly in a negative way.

'The petty, trite things that make you go, "Oh, God, it's not the right size" or "Why is this happening like this?"—that kind of stuff doesn't exist so much here.

School time: The actress and her family live between Malibu, where her children attend school, and their ranch in Santa Fe, New Mexico

Growing up: Aside from son Henry, Julia also has twins Phinnaeus and Hazel, 8, with husband Danny Moder

She also opened up about her decision to distance herself the many perils of living in Los Angeles.

'Around here, I come and go like it's nothing. Los Angeles is such a town of show business, and I'm a terrible celebrity. I find it difficult—it's the beast that must be fed.'

'I remember when you could dress for a premiere just by putting on a cute top. Now you have to be perfect and fabulous in every way, or you're ridiculed.'