The opposing side to my opinion has stated that she herself had a negative experience learning about anatomy in fourth grade. In order to learn about anatomy before middle school, it should be the child's choice. He or she should obtain a parent signature if they or the parent feels they are mature enough to learn about the topic. Anatomy should not be looked down upon as something that someone may find revolting unless you have the reproductive system in mind, but that should not be looked at in a sexual manner when dealing with anatomy. The bottom line: I believe children under middle school ages should learn anatomy if they feel they are prepared because it is not a controversial topic and most can be mature enough to understand the material and take it seriously.
They should at least get introduced to some basic facts about anatomy even if a demonstration (animal dissecting) isn't used at first. Certainly students can learn about the digestive system, respiratory system, and nervous system at the very least. You should know about your own knuts and bolts after all.
There are some kids that can't handle learning about human anatomy. First of all, when it was my first year learning about it (4th grade), I almost threw up in my mouth! I was being exposed to something I could not handle. The next year, I begged my parents if I could skip human growth and development, but they said no. But, most kids nearing their pre-teenage years already know and already have a jump start. They know some things, but they should wait until middle school to learn about them. That is why I think that kids should wait until junior high to learn about things like that.