One thing to do is make sure the kids understand that the Bible is just a bunch of stories. My mom teaches Reform Jewish Sunday school and makes this clear to her students. I make fun of her for cranking out little atheists.

Teaching that the bible is a bunch of stories written by multiple humans over time is not nearly as offensive as preaching atheism. Start there. This bit of knowledge should be enough to get your young relatives thinking about religion, if they want to start thinking about it.