Children as young as six suffer sexual violence in school, MPs heard during a debate on the issue in Parliament.
Tory MP Maria Miller said one mother had told her that her six-year-old was raped by a classmate but her teachers dismissed it as "playful activity".
Another parent told her his daughter had been raped at school.
Minister for Women Anne Milton said parents who felt their child was unsafe should go to children's social care and there remained "much more to do".
The government also said it would issue more guidance to schools on dealing with sexual harassment.
Thursday's debate followed a report published last year which suggested sexual harassment among pupils had become "normalised".
Ms Miller, chairman of the Women and Equalities Committee, said the incident involving the six-year-old was not recorded centrally because the child was under the age of criminal responsibility.
She said the second parent had said girls as young as 12 were encouraging each other to send sexual images of themselves to their peer group and were encouraged to have anal sex by their classmates.
'Epidemic of abusive photos'
Labour MP John Mann described an "epidemic of abusive sexual photographs of girls being circulated on a daily basis around schools" and suggested "schools and teachers have no idea what to do about the problem".
He said: "I get very depressed by the numbers of people - usually of women - who come to see me and I find out what happened to them at school.
"Their parents do not know, they have no idea whatever. These women will not have reported to the police the fact that they have been raped. The volume is so incredibly profound that we have an epidemic in this country."
The debate follows a Women and Equalities Committee hearing last month where schools minister Nick Gibb admitted current guidance does not stop children who sexually abuse other pupils being put back in the same classroom as their victim.
However Mr Gibb said this situation should not happen and said the Keeping Children Safe in Education guidance could include this when it is revised this year.
In September 2015, a BBC investigation revealed there were 5,500 sexual offences recorded in UK schools between 2011 and 2014.
Among these were nearly 4,000 alleged physical sexual assaults and more than 600 rapes, figures from Freedom of Information requests showed.
At least a fifth of offences were carried out by children on children, but details of the rest of the assaults are not known.
Since last year's report, the Children and Social Work Act (2017) has made relationships education for all primary school children and relationships and sex education for all secondary school children compulsory.
Ms Miller called for more "urgency" from government to tackle the issue. Even when statutory guidance is issued to schools, it will still take a full academic year to come into force, she said.
Minister for Women Anne Milton said she hoped new draft regulations and guidance on relationships and sex education would be published in 2018.
However she said this alone was "not sufficient" and "all schools have a legislative duty to safeguard and protect children".
She added: "In a serious situation - a number of serious and harrowing situations have been raised today - if parents or carers do not think that a child is safe, they should go to children's social care.
"Alternatively, if a parent or carer feels that a school is not fulfilling its duty because either it is not following its policies or it has inadequate policies, there is a whistleblowing line with Ofsted and the NSPCC."