TEACHERS are overhearing Tasmanian primary students boasting about having oral sex.
Roz Madsen from the Australian Education Union (AEU) said teachers "felt helpless" at how to deal with the problem, The Mercury reported.
"The students are talking about what they have done on the weekend, sexual experiences that they are having," she said.
"It seems to be happening at earlier ages."
She said at a recent AEU forum, teachers had described what children in grades 4 and 5 talked about.
"They are talking about oral sex and saying they are doing it. Who knows if they are or are just boasting, I hope they are not," she said.
"And the language as well, it's quite explicit, nothing is left to the imagination."
Family Planning Tasmania's chief executive Sue Williams said teachers were "horrified" at the conversations on Monday mornings when kids compared what they had done on the weekend.
"All sorts of sexual activities," she said.
"Oral sex has become the new kissing. It's easy and you don't get pregnant."
She said for some children, their first knowledge of sex was through pornography on computers or mobile phones.
Sexting was also a growing problem, where kids send explicit photographs of themselves to others on mobile phones.
Ms Williams said teen pregnancy remained an issue and the centre had heard of 12 and 13-year-old girls falling pregnant and a 14-year-old giving birth to her second child.
Relationships had evolved and school kids now had "friends with benefits" and multiple sexual partners rather than a steady mate, she said.
Ms Madsen said body image was an emerging issue and teachers were reporting kindergarten kids were worried about how they looked.
In March, Family Planning, the AEU and other groups including Parents and Friends and Relationships Australia will join forces at a forum to call for sex and relationship education to be part of the school curriculum.
The Education Department leaves it to individual schools to decide how to offer this, which Ms Williams said meant the quantity and quality varied dramatically.
"Teachers say there is no central policy so they feel quite vulnerable to take it on," she said.
Education Department spokesman Bob Phillips said parents had a role to play in teaching their children about sex and relationships.
"Schools are only partially responsible," he said.