A teaching union in Birmingham has raised questions about government plans to force all primary and secondary schools to provide sex education.
Rednal-based union NASUWT voiced some concerns about the controversial proposals announced today by the cross-party Education Committee.
The Committee has recommended that the Department for Education develops a plan to introduce "age appropriate" sex and relationship classes for pupils as young as four-years-old.
It would make it a legal requirement for all schools to devote "appropriate curriculum time" for the sessions, which would also include personal, social health and economic education (PSHE).
Previously axed funding to train teachers and school nurses how to teach the subject should also be re-instated, said the committee.
Meanwhile, parents would be given the right to withdraw their child from "some elements" of the sex education classes, MPs revealed.
And parents would be regularly consulted on the content of the classes, while they would be renamed 'Relationships and Sex Education' to emphasise the relationships element of the subject.
The move comes after education watchdog Ofsted found in 2013 that sex education "required improvement" in 40 per cent of the schools it inspected in England.
Chris Keates, general secretary of NASUWT, said the union would cautiously welcome the move.
"We have no problem in principle with what the Committee appears to be saying, however, some key questions need to be addressed," she added.
"Who will determine what is age appropriate? Will academies and free schools be required to implement such provision, given that they have freedom to determine their own curriculum?
"And who will provide the specialist support and training schools need to deliver this provision, given that local authorities and the NHS no longer have the specialist staff and resources to provide this support thanks to savage cuts to their budgets?"
Tory MP Graham Stuart, chairman of the Committee, said the government's current strategy for improving sex education was "weak".
"There is an overwhelming demand for statutory sex and relationships education - from teachers, parents and young people themselves," he added. "It's important that school leaders and governors take PSHE seriously and improve their provision by investing in training for teachers and putting PSHE lessons on the school timetable.
"Statutory status will help ensure all of this happens.
"Young people have a right to information that will keep them healthy and safe.
"Sex and relationships education forms an important part of any school's efforts to safeguard young people from abuse, and is particularly needed to protect the most vulnerable children.
“PSHE builds character and resilience, and will help young people to live happy and healthy lives.”
But he insisted parents would be able to pull their children out of the classes.
“Parents have rights too,” he added. “They must be consulted by schools on the provision of sex and relationships education and must keep the right to withdraw their children if they are unhappy with what the school provides.”