A meeting between education officials and parents took place this week, with parents demanding to know why P2 children are learning about sexual organs “when they’ve only just learned to write their names”.
The five- and six-year-olds at Ladybank Primary, near Cupar, are told how both male and female parts are needed to make a baby.
The early sex education has been introduced because parts of Fife have very high rates of underage pregnancy.
But many parents at the school claim the lessons - which move on to names for genitalia by the age of eight - are too much too soon.
One parent of a P2, who asked not to be named, said: “They’re telling our kids how to have sex when they’ve only just learnt to write their own names.
“It’s absolutely shocking.”
She added: “We all went down to the school after we got the timetables because we couldn’t believe what they want to teach ours kids. It’s jaw-dropping.
“They want to teach six year olds what is needed to make a baby which last time I checked was called having sex.
“Kids are curious and they’re basically telling them how to do grown up stuff at a ridiculously young age.
“It’s no wonder STIs and young pregnancies are on the rise when these children are basically being given a how-to-guide about what’s needed to have sex.”
The concerned resident added: “We were told we can opt our kids out if we want to but the ‘subject areas’ would be touched on in other subjects and we couldn’t pull the kids out every time.”
Scottish Conservative young people spokeswoman Liz Smith said sex education should not be delivered at “the expense of childhood innocence”.
“While it’s important to ensure children entering their early teens are well informed, we shouldn’t do that at the expense of childhood innocence and at an age when they cannot be expected to appreciate the responsibilities involved.”
In 2012, NHS Fife had the highest teenage pregnancy rate for under-16s with 9.2 per cent of every 1,000 girls falling pregnant. It also had the highest rate for under-18s with 47.7 per cent.
And a pioneering sex education project was launched in Kirkcaldy three years ago in a bid to cut the number of teen pregnancies.
It has been hailed a success after noting a 40 per cent decrease in the number of pupils falling pregnant.
Carrie Lindsay, an area education officer with the council, said: “All lessons in our schools are taught at an appropriate level for the age and ability of the child.
“By introducing such discussions in a very simple, upfront, non-sensational way the subject just becomes part of the everyday discussions in the classroom.”