I would disagree on the part of "decades." But, that's irrelevant.
No one is forced to have drag queens to teach their children. There are multiple ways to circumvent this issue. Such as (but not limited to) finding a new class, home schooling, private schooling, and changing schools.
By "Change their language" I assume you mean "gay," "f*g," etc. Well, I would have to say that it depends on the context of which it is used. Words have their meaning changed over time. And when one uses the term gay in the context of "Oh that's gay" they're saying that something is negative or not good the the speaker. While homosexuals also have had this nomenclature for a longer time than the phrase was coined, I believe. You can see how such phrases can be -reasonably- offensive. Just as the term "honky" is a white slur but is also used in conjunction with the phrase "honkey dorey" meaning "all right."
And for your last question. That is a question that you have to ask yourself and understand the perspective of the homosexual. You see, this event is an event where they are permitted to be blatantly and completely open and honest with who they are and not be afraid to show this. If this offends you, don't attend. If it goes by where you work, ask for the day off, but don't say why. There are many ways to avoid this issue if it offends you. I would imagine they respect your right to feel offended, they might feel bad about it, but they will respect it. I would expect, if I were gay, that you would equally respect what I am. You don't have to agree with it, you might feel bad, but that in this hypothetical, that you respect me individuality - that which this country was built on. That is, the right to individual freedom.