A new study has found that just under one quarter of young people in Britain were aged 12 or younger when they first saw internet pornography.
More than half the people who took part in the survey said that porn affects what people expect from sex.
And a clear majority, 74%, said that it particularly affects what men expect from real-life sexual encounters. When asked why, respondents said: "Young men expect young women to behave like the women in porn films."
Nearly 10% of those polled said young men now expect women to be "sex objects".
What may also shock parents is the frequency with which boys access internet porn. Almost half those who took part in the study said they look at online porn every day or quite often, defined as once and week.
Only one in 10 young women look at online porn that frequently and half of them said they don't ever look at it.
"It's unrealistic" was the most common answer when people were asked what was the worst thing about porn. But at the same time many young people, particularly girls, say they watch porn to learn about sex.
The study will form the basis of Porn: What's The Harm? on BBC Three this Thursday evening at 21:00 BST.
The survey will be adapted to a set of learning materials to be used in schools to teach people about pornography and relationships.