Zac Efron says parents must be "passionate" about sex.

The 'High School Musical' actor - who is dating his co-star Vanessa Hudgens - says it is important for adults to be enthusiastic when discussing sex and contraception with their children.

Speaking about his talk with his father David Efron, Zac said: "I just feel like my dad, at one point, had that conversation with me and my little brother, and always delivered it very well. He was very passionate about it."

The 21-year-old hunk recently admitted his mother Starla is not quite so relaxed about addressing his sex life and was upset when she saw a photograph of him and Vanessa apparently leaving a sex toy shop.

He explained: "My mom is like, 'Zac, what did you buy in a sex shop?' I was like, 'Mom, calm down, it's not a sex shop.' She wouldn't have any of it.

"She's like, 'I knew you were being sexual!' But she understood. My stocking was full of condoms this Christmas. She buys me the economy box."