Under the news plans children would be taught the names of body parts and basic ideas about different relationships.
Brook, the fpa (formerly the Family Planning Association) and the Sex Education Forum said the basic sex education children currently receive in science classes is inadequate.
They claim a "gradual education" from a young age will help stop children rushing into sex, and reduce abortion rates and sexually transmitted infections when they reach adolescence.
Simon Blake, chief executive of Brook, said: "Many young people are having sex because they want to find out what it is, because they were drunk or because their mates were. That's just not good enough for young people.
"If we get high quality sex and relationships education in every primary and secondary school across the UK, all the evidence shows teenage pregnancy rates will continue to fall and will improve young people's sexual health.
"Whilst sex and relationships education continues to be patchy, another generation of children and young people do not get the education they need to form healthy relationships and protect their sexual health."
However, the recommendations have angered family campaigners who claim the views of parents and teachers are being ignored.
Norman Wells, director of the pressure group, Family and Youth Concern, said: "What this is really all about is the sex education establishment trying to force schools to do something many parents - and many teachers - are uncomfortable with.
"It's quite extraordinary that the fpa and Brook should be calling on the government to impose something on every child in every school that has no proven benefit whatsoever.
"It's vital that parents' views should continue to be respected and that schools should remain sensitive to parental concerns on such a controversial issue."
At present, primary heads and governors decide whether or not to provide sex education and what it should involve beyond the compulsory requirements for science lessons set by the national curriculum.
Schools must have policy on whether or not they provide sex education, which is usually delivered in personal, social and health education (PSHE) lessons. If they do, parents have the right to withdraw their children from classes.
The charities are advising the Government's review of Sex and Relationship Education (SRE) in primary and secondary schools.
A spokesman for the Department for Children, Schools and Families said no final decision has been made. The steering group, jointly chaired by Jim Knight, the Schools Minister, will make its recommendations to the Government later this month.
The spokesman added: "Effective sex and relationships education is essential for young people to make safe and healthy choices about their lives and prevent early pregnancy and sexually transmitted infections.
"That is why Government is currently reviewing the delivery of SRE in schools to improve the quality and consistency of provision to young people."
