All children must learn about same sex couples regardless of their religious background, the head of Ofsted says.
Hundreds of parents protested outside a Birmingham school against it teaching pupils about same sex couples and gender identity.
Ofsted chief inspector Amanda Spielman told the BBC it was crucial children were exposed to differences in society.
She said it was important children knew "there are families that have two mummies or two daddies".
Parents of Muslim and Christian faith have held demonstrations outside Parkfield Community School in the Alum Rock area of the city, where children are taught about same sex couples through story books.
Protesters have claimed the lessons, part of the "No Outsiders" programme, contradict their faith.
They argued assistant head Andrew Moffat, who started the lessons and is gay, has been "promoting personal beliefs and convictions about universal acceptability of homosexuality as being normal and morally correct".
But Mrs Spielman said the lessons were "about making sure they [children] know just enough to know that some people prefer not to get married to somebody of the opposite sex and that sometimes there are families that have two mummies or two daddies".
"It's about making sure that children who do happen to realise that they themselves may not fit a conventional pattern know that they're not bad or ill."
In light of the protests, Mrs Spielman said there needed to be a "careful exploration of the middle ground" but lessons covering LGBT topics were important.
One mother, who wished to remain anonymous, accused the school of "planting ideas" in children's heads.
Her daughter attends Parkfield School and she said she was too young to be taught "what goes on in someone's bedroom".
"It's something that we would like to teach our children ourselves," she said. "It kind of feels like they're forcing it upon us."
She denied being homophobic but said "it's just not what we're about and we don't agree with it".
Mr Moffat told the BBC he had been receiving threats and "nasty emails" from parents who disagreed with the programme.
Mrs Spielman argued the lessons were less about "endless sex education" and more about understanding differences in society.
"The essence of democracy is that we don't all get our way," she said.
"We accept majority decision which means there will always be things that some of us don't like, but that is the very essence of it - accepting that we can't have 100% of what we want."
Solutions, she said, would be found in "sane, rational discussion, not protest".
However, the BBC understands more protests were being planned and some parents have said they would write to the government demanding a change in equality legislation.
The change, they hoped, would enable schools not to teach subjects that were not in line with religious beliefs.
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