On a recent Tuesday in August, a group of preschoolers and elementary school pupils in Tokyo listened carefully to their cram school teacher’s explanation about what would normally be a taboo subject for kids this age — sex.

“Sperm, ovum, sexual intercourse, fertilization,” the children stood up and chanted in unison.

The group of 18, ages 4 to 11, were attending a class at Terakoya Annex, a cram school in Taito Ward that provides innovative education, including about sex.

In Japan, such a scene is rare, if not unheard of.

Although the education ministry’s curriculum guidelines for public elementary and junior high schools explain what fertilization and pregnancy are, they refrain from using the term “sexual intercourse.”

In a section about first-grade junior high school students, the guidelines say: “As they are on the onset of puberty, (schools) should take up issues of fertility and pregnancy but not the process of how they become pregnant.”

The ministry believes sex education at an early age could stimulate children’s curiosity and lead them to experiment with sex.

But given today’s relatively easy access to adult content online, children face a greater risk of being exposed to the process without being educated about it.

“Unless parents bring this subject up at home, children don’t have any chance to talk about sex,” said Yuya Imai, a school staffer and spokesman for Terakoya Kids, the parent company of Terakoya Annex. “This program is aimed at familiarizing children with the topic and they really enjoy learning about it in a fun way.”

Sexual education is part of the program at Terakoya Annex, which opened in late July. It also provides unique classes on writing, English and history. For instance, at one culinary lesson, attendees re-create dishes from past periods of Japanese history based on recipes from back then.

In the lesson on sex, the children learned that sex education is related to how they’ve been brought into the world, and listened to a simple explanation about the process of copulation, sperm motility and the role of the ovum. They also used cards to learn about fertilization and took quizzes.

Nami Nojima, who handles the sex education lessons at Terakoya Annex, has 15 years of experience as a nurse and also runs a group called Pantsu no Kyoshitsu Academy Association (loosely translated as Pants Classroom Academy). The group conducts classes for adults on how to discuss sex with their children.

Nojima learned about the subject by openly talking about it with her parents. But that’s not the norm in Japan.

“Only three of 3,000 women who have come to my lectures said they had spoken about it at home,” she recalled. “Many women said the atmosphere in the room would always get eerie when a TV show they were watching with their parents aired a kissing scene.”

What inspired her to launch the program was the abduction of a child in her neighborhood. The incident shocked Nojima and prompted her to think twice about how she could protect her three daughters from sex offenders.

She is also concerned about the lack of detailed sex education in the school system.

“When I asked my daughters what they would do if someone came up to them and asked if they can touch them, they didn’t know what to do. But they said they might have gone with a stranger if he or she asked them to,” Nojima recalled. “They might do so if they don’t have enough knowledge about the risks. And you can’t explain it without telling them about sex.”

Nojima also lamented children’s public exposure to sexual content, pointing to websites with pornographic content attached under online cartoon games for children and referring to adult magazines available at convenience stores.

“Despite that, sex is still taboo in Japanese society,” and the sex education program is outdated, she said.

“Thirty years ago children weren’t taught about sex (by their parents). . . . But there is a greater risk of exposure from adult content now so we can’t learn from our past experience,” she stressed. “Sex education requires a new approach that would fit with the times.”

She suggests that the best period to start engaging children in conversation about sex is around the ages of 3 to 10, before puberty — when many children start to avoid talking with their parents.

“Younger children may not understand everything but they’ll get familiar with expressions related to sex and they’ll know it’s okay to talk about it,” Nojima said.

During the August class, the children were given advice on how to protect their “sensitive zones.”

“Noooo!” they said loudly in unison when asked if it’s permissible to touch or hurt the sensitive zones of others, even during a play, and whether it’s okay to show their genitals to strangers.

They also took part in a drill on how to react if a stranger tries to sexually assault them.

Rio Sugiura, 6, said she was aware that adults could try to harm her.

“I’m scared that someone might kidnap me,” she said shyly, adding that her parents often warn her not to talk to strangers.

“It’s important to learn about sex so you can learn how to protect yourself,” said Shin Horiguchi.

“I also learned to call for help if someone tries to abuse me,” the 10-year-old boy said.

Kaori Wakabayashi, 34, brought her 4-year-old daughter to Terakoya from Kawasaki, believing that attending the class will help prevent her daughter from becoming a sex crime victim. She said parents can’t let their guard down when they hear about kids being victimized by preschool teachers.

“Once my kids enter elementary school, they’ll probably spend more time on their own so the risks will be higher,” Wakabayashi said.

She believes the class might even help her talk openly about sex with her children.

“If they know the terminology, I’ll feel more comfortable and can more easily bring this topic up in a casual conversation,” she said.

The organizers have been flooded with queries from parent-teacher associations in elementary and middle schools, which can’t officially organize such classes, as well as from families across the country.

Nojima believes discussions about sex can also help families strengthen their bonds.

“Sex doesn’t only have negative connotations, it’s also about bringing new life into the world and about giving love,” she said. “The Japanese struggle with showing their feelings, but during discussions about sex, parents can tell their children why they were born and how much their existence means to them.”