Actually, children shouldn’t have to wait until they start school to learn that there are LGBQT people and that they are are as important as, and have the same rights as, every other person. Likewise, they shouldn’t have to wait that long to find out that there are people with different religious beliefs, political beliefs, skin colors, etc. who are equally important as they are.
I remember teaching a junior high Sunday School class and happened to mention atheists. I was amazed to find that no one in the class knew about them. Different religions, yes, they knew about that. No religion or no belief in a God? Flabbergasted them, and me. I couldn’t believe they’d reached the age of 12-14 without ever hearing about or meeting an atheist. Just one of many reasons I stopped teaching Sunday School.
The US is not a melting pot, nor is the world as a whole. It’s more like a stew, with many different ingredients that blend together to make a meal that’s better as a whole than any of its parts.