NO!!!! Absolutely unacceptable. I will homeschool if you pass this. And I will also actively work with other parents to not only have you removed from your position, but also have this removed from the schools. Elementary and middle school children are too young and too easily confused. I think this is a subject that needs to be left to parents. I do think it is totally acceptable for you to put together a curriculum that parents who ask or seek guidance in explanation this to their kids, can get easy access to.
But this is NOT a discussion for young children and should NOT be taught in school. Not everything is the purview of the state in regards to education.