I could see if it were age appropriate, because unfortunately, kids do need sex education earlier. Age appropriate sex ed for the preschool should be about setting boundaries and learning proper names. I think it's important for children to know that certain areas of their body are private and that they always have the right to say no to touching that makes them feel uncomfortable.

We had a problem with a little girl in my son's soccer class last spring. She kept hugging, licking, and kissing my son, even though they're both only 3. I had a hard time getting the high school age girls who taught the class to put a stop to it because "Oh, isn't that so cute! They're like boyfriend and girlfriend!" took precedence over my son's acute discomfort and inability to participate with a 3 year old girl glued to him. I ended up formally complaining to the management and transferring my son to another class because the teachers were encouraging the little girl.

It seems like while they're not common, there are parents who encourage their children to behave like this little girl because they believe it's "cute", regardless of the other person's discomfort. I also think it sets a bad precedent to allow a child to continue touching another child in a way that makes them uncomfortable, while encouraging the other child to not make a fuss.

That sounds like a badly behaved little girl who's bad behaviour was being ignored on the basis of being "cute". Which is inexcusable. For both your son and her own learning experience. We all need to know what is and what is not acceptable behaviour.

However, it wasn't sexual behaviour. Touching, at preschool age, is not sexual. It can certainly be inappropriate -- in the same way that name calling, throwing rocks, or disrespecting classroom materials is inappropriate. It is not the right way to behave. You must be taught to respect people's boundaries. But this does not require sex ed.

I have a four year old. He knows what a penis and a vagina are. He knows that boys have one and girls have the other. He knows that these are "private" areas, not to be touched by other people unless by a doctor in the room with Mommy or Daddy. These are simply life lessons. He also knows to wait for the walk signal and look both ways before he crosses the road. He knows to chew his food properly to avoid choking. He knows how to get dressed.

What I'm getting at is that at four years old, SEX education is not necessary. Why complicate things for our children any more than the media and modern society already have? Why not let them be children for awhile? I don't want my son worrying about sex, about "making babies", about marriage and relationships. He's four! So, I still feel that preschool is far too young for this...

This is why it is "Sex and Relationship Education." They are not advocating teaching 4 year olds the details of how babies are made or what the sex act is; they are talking about including age-appropriate information in educational programs. This includes things like the differences between genders (boys have penises, girls have vaginas, mommies (adult girls) have breasts, daddies don't, etc). Lots of 4 year olds have younger siblings -- what did mom & dad tell them about how that sibling arrived, and what that baby bump was?
I remember being about 6 and reading a book that told me how babies were made (it had cartoon sperms wearing tophats in it!) -- there was nothing explicit in it, it was all biology, tailored for my age group. My mom tells me that about the age of 2 or so (probably around the time my sister made her appearance), I started asking about where babies came from. She told me that they are made by a mommy & daddy when they love each other very much, and left it at that -- perfectly appropriate for a 2 year old. As I got older, I got more detailed information.
I don't have a problem with this type of information being included in general educational programs, but I would sure want to know exactly what they were teaching and how it was being presented.