I would say that overt sexual education at that age is inappropriate. However, children have questions and those questions should always be answered as factually as possible.

Here's a real life experience of my childhood. A little girl came to my elementary school class, back in the early 1970s, in Jacksonville, Florida – of course, it was Florida… even then. 🙄 Her mom was white and her dad was Black. She was the first interracial child they'd ever seen. The children had lots of surprising questions and repeated tropes they'd learned at home. Those children had not been and would not be taught the facts of racism and inequality, nor had they learned tolerance at home. Teachers had to answer those questions and address those tropes – or they'd have been complicit in that child's abuse by her peers.

If parents are going propagate old tropes and all the harm that goes with those tropes to children, then yes, it is the school's business to teach kids that young. Facts, compassion, and tolerance are the only ways to lift future generations out of the ingnorance and bigotries of the past.