The star told a Cannes press conference she likes to make "bold" choices, as if she were at the start of her career.
Kidman said while she doesn't have to work, she does so because of her passion for cinema.
The star of The Killing of the Sacred Deer, in competition at Cannes, said her young children will be banned from seeing the dark psychological thriller.
Kidman has two grown-up children from her marriage to Tom Cruise and two younger daughters with her current husband singer Keith Urban.
"My (younger) children have very little understanding of what me or my husband do. Their lives are obviously far more important!"
She added: "I'm at that stage in my life where I still try to act as if I'm 21 and starting my career.
"At this stage of my life, I'm just trying to stay very bold and open and try things and support film-makers I believe in."
The Killing of the Sacred Deer features an eminent surgeon Steven Murphy - played by Colin Farrell -  who adopts a teenager into his family. Things start to go horribly wrong when the boy turns against Murphy.
Kidman plays ophthalmologist Anna Murphy, who is married to Steven.
It's directed by Yorgos Lanthimos, the Greek filmmaker behind indie hit The Lobster, which won the Jury Prize at Cannes two years ago. Farrell also starred in that film.
Kidman said she was "hypnotised" by Lanthimos' script.
She has four projects showing at the festival this year, but said: "That's a confluence of events - that's not something I was aware would be happening."
Her other Cannes showings are in The Beguiled and How to Talk to Girls at Parties, as well as the second series of TV drama Top of the Lake, from Jane Campion.
She singled out Campion for praise, saying she had been a friend of hers since the age of 14 and that "she discovered me, basically."
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Oscar winner Nicole Kidman says she still acts like she's 21 when it comes to acting roles.