The earliest the material is going to be presented is to grade 4 students. Specifically, this is the material dealing with the process of pubrity. It might sound early, but this is completely justified when the age children are entering pubrity has been shifting lower over time. You can't simply assume it's still the same way it's always been, when the age range now is in the area between 8 and 14, girls tending to be earlier.
The education moves towards the subject of sex in grade 5, but the material there is primarily limited to telling them to stay away from things that could ruin their lives or the lives of others. Sharing sexual pictures online, for instance, or cyberbulling related to sexuality.
Grade 6 is when sexual intercourse starts being on the table. What it is, why it is, and how it is gets discussed, and the idea of consent as something extremely important are all introduced. The consent part isn't just with regards to sex; the curriculum is to teach consent more broadly, the importance of respecting others' feelings, and how to tell if someone really wants something via nonlinguistic communication. (Saying 'yes' but seeming uncomfortable with it, for instance.)
In grade 7, kids are--that's right--to be taught the importance of not engaging in sexual activity. Sexually-transmitted diseases and infections are a real danger in our world, as are accidental pregnancies. Keeping kids moving into their teenage years, where they are inevitably going to try to experiment, from travelling down harmful routes while also not punishing the desire to explore is the goal.
Is this really all so horribly objectionable? Parents aren't magically great at teaching about sexuality simply by virtue of being parents. Some do it wonderfully; some have a trusting, open relationship with their children wherein these subjects can be discussed and learned about accurately. The problem is that not everybody is like that. I'd be willing to wager the majority aren't.
This isn't about corrupting children, it's about keeping up with the times. The way kids are introduced to these subjects, and when, has been changing. The dangers are changing. Please don't stick your head in the sand and ignore this because you insist that your plan on what to do is superior to--and should not ever be challenged by--hundreds to thousands of experts on biology, human sexuality, parenting, and teaching.
Withholding information about sex and sexuality will not keep children safe; it will only keep them ignorant. Providing a foundation of quality sex education is the only way to ensure that young people will grow into sexually healthy adults. Sexual education happens whether we know it or not. It is much better to take charge of the process.
I am not saying don't teach it at all, I am saying to not teach it at such a young age. Little kids are so innocent they shouldn't learn this half of them don't even know how to spell and they're going to learn this!?! Its good to learn about it so you know what it is but why at such a young age! I say if your going to teach it then do it when the kids are in a higher grade!