Anyway, I'm not very familiar with Creationism, but if it is true that it is not true science, but religion disguised as science, then I don't want it taught in schools either.
It is not science. It has nothing at all to do with science. It's about trying to prove a pre-existing conclusion by acknowledging that which supprots the conclusion and dismissing that which does not, and it's further complicated by extreme dishonesty and ignorance such that Creationsits put forward "evidence" that in reality supports nothing approaching what they believe it to support.
Not only would children miss out on learning true science, but it would also violate our principle of separation of church and state.
This is why Creationism and it's inbred stepchild Intelligent Design have been excluded from public classrooms by the Supreme Court.
I do think, though, that before any science that conflicts with major religions is taught, the teachers should explain the conflict,
That's unfortunately a bit unreasonable. Which major religions? Christianity, Islam, Judaism, and Hindu? Which denomination of each? Some Chrsitians have no problem with evolution and an old Earth; many others do. Hindus have no issue with an old Earth, but would conflict basically everything else in the other major religions.
Why not simply teach science, with a statement by the teacher that what they are learning is what can be independantly verified to be highly accurate through methodical observation and testing, along with an in-depth examination of teh scientific methiod and how/why it leads to accurate representations of reality?
Why not simply teach science?
and also define a scientific theory. And quiz the kids on the definition of a scientific theory. I think some teachers may just present evolution and the big bang as flat-out, absolute truths.
It's worse than that - many teachers don't understand evolution themselves. Students are rarely exposed to a real, solid class on evolution until the college level, and that only if they take biology classes. High school level biology may spend all of a week on evolution, and many students still walk away thinking that a "mutant" is something akin to the Teenage Mutant Ninja Turtles, or that evolution will eventually lead to the world portrayed in the "X-Men" movies. When they're taught that "birds became dinosaurs," they frequently believe that they are being told that, literally, a T-rex transformed into a pigeon - this is why people like Ray Comfort expect evolution to result in weird half-dog, half-cat chimeras.
The quality of science education needs to be drastically improved in this country, and that's not going to happen when religious institutions are allowed to interfere with scientific instruction. We tried that back when the church burned heretics for suggesting that the Bible may not be a viable historical account; the results for humanity were less than ideal.