I believe the best spiritual inoculation method for children simply is creating an open environment where they feel comfortable asking anything - and teaching them what you consider to be correct principles - and being willing to entertain unique perspectives from them.
When your children ask a question, do you give them an answer - or do you ask them what they think? When they tell you what they think, do you "correct" them or merely validate their still immature understanding - or do you try to build on their understanding and help them see multiple perspectives? Do you encourage them to think for themselves - or merely to memorize your or others' answers?
When you read the scriptures with them, do you just read as much as you can cover - or do you discuss every verse and/or passage to make sure they have a chance to understand what it says (and, in some cases, differing opinions on what it says)?
I could go on, but the key is pretty simple. I just wish, sometimes, it was easy.