FWIW, I learned the same in 4th grade, circa 1968 in a public school in St. Louis. This isn't new, if that helps.
We learned in fifth grade (not the sex part). Here, we actually have the PARENTS/a different group teach it as an optional after school meeting (note 2 sessions, not continuously) where those who do attend are strongly urged to attend with a parent. At least half the kids have a parent present (and yes, all parents are notified of it). Let me tell you, as a teacher, I'm perfectly fine with not having to teach sex ed. In an elementary school, I don't feel it should be a teacher's job. There's other, more important things like reading, writing, and math to teach. And 4th grade at a Catholic school is actually earlier than I've ever seen it for any public school in the areas I've been in.