The new relationships and sex education (RSE) guidance for schools from gay lobby group Stonewall is too narrow, the Christian Institute has said.
The Christian Institute said that the voluntary guidance may leave primary schools feeling intimidated into introducing LGBT teaching not required by Ofsted.
The new guidance from Stonewall has been released ahead of the introduction of the new mandatory RSE curriculum in September 2020, which includes teaching on LGBT relationships and issues.
Stonewall said the new guide is designed to support teachers in delivering "LGBT-inclusive" education and tackling anti-LGBT bullying.
Recommendations to schools include using LGBT families as examples in classroom exercises.
"For example: 'Mark's dads increase his pocket money by 10%. If Mark had £2 before the increase, how much pocket money does he have now?'" the guidance reads.
In its recommendations for Religious Education lessons at Key Stage 2 - covering children aged 7 to 11 - schools are encouraged to hold Pride celebrations and learn about different wedding ceremonies, and suggests for a classroom activity children creating an order of service for a gay wedding or civil partnership.
RE lessons could also teach young children about religious naming ceremonies for transgender people, schools are told.
"When learning about religious naming ceremonies, teach that some trans people choose to have a 'naming ceremony' or blessing following their transition," it states.
Pro-LGBT books recommended in the guide include 'And Tango Makes Three' for maths, science and PSHE lessons, and 'King and King' for RE. In Design and Technology classes, the document suggests that Key Stage 1 classes for children as young as five can teach about the 'LGBT flag', 'trans flag' and the 'bi flag'.
The document suggests that Ofsted will be watching schools to make sure their curriculum is LGBT inclusive.
"Making your curriculum LGBT inclusive plays an important role within a whole-school approach to tackling homophobia, biphobia and transphobia," it reads.
"Ofsted, SIAMS (the Statutory Inspection of Anglican and Methodist Schools) and the Independent Schools Inspectorate (ISI) will look to see that you are doing this."
The Christian Institute said, however, that there was no requirement by Ofsted to include LGBT teaching across the curriculum and that the education watchdog has said it would respect the autonomy of schools.
The Christian Institute's Education Officer John Denning said: "This document seems designed to intimidate schools. Ofsted isn't specifically looking for the type of content Stonewall recommends.
"The regulator is clear that bullying should not be tolerated, but they don't present such a narrow perspective as Stonewall.
"Schools must educate, not indoctrinate. Our new Equipped for Equality booklet helps parents understand what schools can and can't do in the name of equality and human rights."