Children as young as three are using homophobic insults and their teachers need more guidance in how to deal with it, says the National Union of Teachers.
The union said "gay" remarks were common in primary schools and that early-years staff needed to challenge children's homophobia and gender stereotypes. A report to the Department for Education and Skills said: "It is too late to wait until primary school to challenge prejudice and intolerant, abusive language."
The NUT's head of education John Bangs said: "Of course we have to be sensitive, but we have to point out it is OK for men and men to be together and women and women."
The union wants information about good practice in dealing with homophobia to be included in the Government's Early Years Foundation Stage curriculum.
Paul Patrick, the co-chairman of Schools Out, which promotes sexual equality in schools, said: "All the research says homophobic bullying starts in primary schools. Gender stereotypes and sexuality are policed in the playground by children from a very young age. The longer you leave that to get ingrained, the harder it is to challenge."
He said the Government needed to update the way it promoted family life by including families with gay or lesbian members.
He said: "Teachers are nervous about how to deal with this and don't feel they get enough support."
Catherine Thompson, head of Hertford infants in Brighton, said although homophobic comments were rare in the school, more advice and information on good practice would be useful for newly qualified or inexperienced teachers.
She said: "Younger or more inexperienced teachers would welcome guidance on dealing with this kind of sensitive issue."
The NUT's comments came in its response to the Government's Early Years Foundation Stage consultation document.
The union said some members were worried about the blurring of boundaries between early-years professionals and teachers.