Despite what people may think, and how we all feel that age is still too young and innocent to know, think about, or care about such things... the truth of reality is the fact that so many kids that age already have caught onto and heard about these things.
How old were most of us REALLY when we starting becoming aware of these things, huh? All that hush hush grown up stuff that we weren't "supposed" to know about, but to some degree we already did and, as normal kids, were naturally curious. Very few people are probably entirely innocent and unaware until age 15 or 18. And if they were...their parent must have kept them away from the world like a prisoner.
Kids don't live in a bubble of isolation. They interact with other kids most days of the week, they and/or friends have older siblings and other friends who know things and being kids they probably aren't going to keep that info to themselves. It is impossible for a large portion of them, maybe even the majority, to not come across this info already by that age. Problem is, it's generally coming from their peers and the information may be pretty faulty or be received in a way that is. The wrong idea may be harmless in some ways, but in others... well, that's how you end up with pregnant 12-year-olds.
As much as 5th grade sounds too young, because it IS too young to have any involvement, and I do not think kids should be receiving ALL the little details... By age 10/11 of that age group, however, a certain amount of basic information, for a group of kids on the cusp of hitting puberty (and some probably already reaching it), an AGE APPROPRIATE amount/level of basic info is probably the smart thing to do in this day and age.
Parents and society may want 10-year-olds to remain little kids until half way into their teens, but that's just not what the reality of NATURE, beyond our control, is actually doing. This age group is standing at the gates of that period in which they will grow into young adults. And not withholding things from them will only help many of them keep out of trouble where these things are concerned, as lack of info only makes curious kids get themselves into more of it.
So yes... it sounds so young, but it's probably appropriate if it's age appropriate info and parents are of course given the right to opt out.
A lot of sex ed, however, is not about telling them how to do it, but is about personal body stuff, so it isn't wrong to prepare them for the upcoming (or already started) changes they will experience. I don't see the harm in a focus on that part. The less they're left with a lack of info, the better.