Charlize Theron says her ''free time'' is devoted to her son.

The 'Million Ways to Die in the West' actress gave birth to Jackson two years ago and admitted becoming a mother has been a ''natural'' change for her.

She told the Mail on Sunday newspaper's Event magazine: ''It's a beautiful change, one that is completely natural.

''Obviously, Jackson is my priority now. If I have free time, he's the one who gets it.

''Not because I have to, but because I can't wait to be with him. He gets to be the number one in my life.''

The star - who started dating Sean Penn in February - also revealed her and ex-boyfriend Stuart Townsend's son has given her the chance to go back to her dancing roots after an injury cut short her professional ambitions.

She said: ''I still dance in my living room every day. I have a lot of 'Mama, let's dance!' going on in my house right now.''

When she's not relaxing with her family, Charlize said she enjoys getting time to herself during filming because it lets her catch up on music and books she might have missed.

She added: ''I always love when I'm on location and I have that bit of trailer time to myself.

''I'm constantly sharing stuff with my friends and that's predominantly how I get my music. I recently played Pharrell William's album, which I thought was really great.

''And I love reading. I just re-read 'Outliers' by Malcolm Gladwell, the book about statistics and looking at numbers, and the coincidence - or it's not a coincidence - that birthdays play a role in success. It's fascinating.''