Schools in England will be banned from teaching sex education to children under the age of nine, under government proposals.
The BBC has not seen the new guidelines, but government officials said they include plans to ban children from being taught about gender identity.
If asked, teachers will have to make it clear that they disagree with gender ideology.
Legal guidance on relationships and sex education, which schools must by law follow, is currently under review.
The National Association of Principals previously expressed concern that the review was “politically motivated” and said there was no evidence to suggest a broader problem with students being presented with age-inappropriate material.
The review was published by Chancellor Rishi Sunak Following concerns that some children were being exposed to “inappropriate content”.
The government believes clearer guidance will support teachers and reassure parents.
The proposals, due to be published on Thursday, will set out which topics should be taught to students at which ages.
All secondary schools in the UK are required to teach relationships, sexuality and health education, and from September 2020 relationships education will also be compulsory in primary schools.
Under current guidance, it is up to primary schools to decide whether they need to cover all aspects of sex education to meet the needs of their students.
Last year, more than 50 Conservative MPs wrote to the Prime Minister claiming that children were being “indoctrinated with radical and evidence-free ideology about sex and gender”.
Separate guidance issued last year said teachers must notify parents if a child wishes to change their gender identity at school.