The head of the Girls' School Association, Dr Helen Wright, will tell delegates at the GSA conference in Bristol today that parents who allow their young daughters to dress provocatively "can't tell right from wrong".
Dr Wright will tell the conference that "mini-me" clothing is a sign of modern society's eroded values.
She will add that it is "intensely wrong" but also that mums and dads are not solely to blame, as they may have been failed themselves by a poor education and lack of teaching of moral standards, leaving them unable to see it is wrong.
Dr Wright - who is the headteacher at St Mary's Calne boarding school in Wiltshire - will blame TV and magazine imagery for making people think that certain standards of dress and behaviour are normal:
"There are all these images in magazines and TV - if you're bombarded with that, you're going to think it's normal, and actually it's not. It's becoming twisted."
Previously, Dr Wright has warned that shows like the X-Factor glamourise bullying and arrogance, and can damage children.
The Evening Standard reports Dr Wright as saying she wants children as young as four to be taught how to deal with sexualised imagery, and the daily stream of "physically perfect" women they see - claiming that a child will see more in a day than her grandmother would see in her whole adolescence.
Dr Wright said: "You have to start in primary school, right from an early age. Almost soon after they are born."
Do you agree with Dr Wright?