You are putting up a strawman to argue. The point is, you can't force on people something they do not desire. If the parents do not want their children to participate in the LGBTQ+ activities, they should have the option to "opt out". Which is a perfectly reasonable request, since they are only asking for it for their own children. Similar to how you can "opt out" of saying the pledge of allegiance.Again, simply knowing gay people exist isn't going to destroy these kids' brains. All schools should prepare kids for reality.
In Finland most children speak 3 languages, understand core math, and are media literate. They also know what LGBTQ is and function as perfectly normal individuals when they grow up.
I understand having a moral disagreement with the existence of the LGBTQ community. But pretending they don't exist is as dumb as trying not to teach children physics because you don't believe in gravity or a spherical earth.
You do a disservice to the kids by obfuscating the realities of the society they live in.
If you want your freedom to participate in those activities, you also need to respect the freedom of those who do not desire to participate.