re: My son was getting brainwashed at school and I couldn't articulate an argument.

Depending on the topic, PragerU has some great videos that are really simple for anyone over 10 to understand on a number of subjects.

Also, your rules may be different than ours. But I have told my oldest kid it is ok to question things or challenge the teacher (respectfully) on anything that he either knows to be different or has a different perspective. (Again without being rude or anything like that). I know for him, he kind of enjoys that, and being able to debate ideas.

Ultimately, if you are a conservative, you want your kids to be able to formulate their opinions on their own. Parents should teach them critical thinking skills, objective truth, how to rrad and interpret history in context and time, etc. Once they have that foundation, they will be able to hold onto their beliefs through anything like college, etc. (In fact these experiences may further strengthen these beliefs)