Updated

Nicole Kidman's latest role is extremely close to her heart.

The 49-year-old actress stars in Lion, in which she plays a mother who adopts her son from India after he's found on the streets of Calcutta at just five years old. Years later, her now grown-up son, Saroo (Dev Patel), sets out to find his lost family.

"I can see now, for Lion, that it was important to me because I'm a mother with adopted children," Kidman tells Town & Country for their December/January issue.

WATCH: Nicole Kidman, Dev Patel Give Roaring Performances in 'Lion' First Look

Kidman has two adopted children with her ex-husband, Tom Cruise -- 23-year-old Isabella and 21-year-old Connor. The Australian star also has two daughters, 8-year-old Sunday and 5-year-old Margaret, with husband Keith Urban.

"This movie is a love letter to my children," Kidman says. "[My character] Sue is deeply maternal and full of unconditional love, which is beautiful."

Chrissy Teigen: John Legend was a 'notorious modelizer'

"That's why I wanted to do it. I relate to that," she continues. "I feel that for my own children who are adopted. It's not about anything else other than 'I wanted you.' It's that deep and personal, and whatever your journey is, I'm here to love and support you. That's what I connected to."

These days, the Oscar-winning actress says she only picks projects that spark her passion.

"I'm so spontaneous -- sometimes to my detriment and sometimes my benefit -- but it's how I've always been," she shares. "My husband never knows what I'm going to choose. And then he'll ask me to explain why and I can't!"

And she's also never been one to follow the norm.

"The mistakes I've made have always involved people not matching the extreme artistic desire -- when I've tried to be a bit more homogenized, or tried not to be as bold," she notes. "When I've been guided into places that don't suit what I am intrinsically -- that's when it doesn't work out���I've been the same way since I was 14. I don't conform. That's just my nature."

Topless snap of 'Real Housewives of Orange County' star leads to trouble

Last September, Kidman revealed she keeps in touch with her children with Cruise via more modern methods, when she was asked by DuJour about her use of the Internet and technology. "I have four children, so to stay in touch with them is very important," Kidman told the magazine. "I'm definitely engaged in it but I don't let it rule my life."

As for reports that she has a complicated relationship with Isabella and Connor due to their Scientology beliefs, Kidman told The Hollywood Reporter in 2013 that she completely respects their religion. "I've chosen not to speak publicly about Scientology. I have two children who are Scientologists -- Connor and Isabella -- and I utterly respect their beliefs," she said.

WATCH: EXCLUSIVE: Nicole Kidman Reveals Her Favorite Red Carpet Looks Ever, Birthday Plans for Keith Urban

Kidman recently reflected on her marriage to Cruise, whom she married when she was 23 years old. The two were married for over a decade before splitting in 2001.

"I was so young when I got married," Kidman acknowledged to Red magazine. "I look back now and I'm like, 'What?'"

"You look at Taylor Swift, I mean, how old is she? She's 26," she added. "I had two kids by the time I was 27 and I'd been married for four years. But that's what I wanted."

Watch below: