I think first grade is a bit early to learn about AIDS and STD's. I think fifth or sixth grade should be safe. Let's not forget that the "fastest growing" group of HIV infections is heterosexuals.
This is a sarcasm tag: (s)(/s). We use this on FR when we make statements that suggest 10- and 11-year-olds need to know about STD's. Otherwise, people might think we're interested in having sex with children that age, and that would be disgusting.
That ol' myth has been shot down many times.
Realize that it was fake statistics to create that...for example, they have changed the definition of AIDS many times, along with HIV infections, and "heterosexual," etc. Male immigrants from certain Africa nations were suddenly automatically categorized as "heterosexual" even if they were having sex with men. The majority of IV drug users getting HIV are heterosexual, but why is that relevant to the sex arena?
Truth is, it's very rare for heterosexuals to contract HIV without IV drug use or without homosexual contact (or contact with someone who is involved in such behavior).
How about just providing instruction to kids that "adult" and forbidden activities are to be avoided?
Let's forget your platitude and not forget that it is activities rather than innate characteristics that spread the disease and that brokeback sexual activity and intravenous drug use are the most probable methods of transmission.