I worry a lot too. Who doesn't? I'm an LDS mom too- and I do worry about teaching the the right things. The things that the church stands for and the morals that I want them to have. I think, as important as it is to talk to your older children, it's just as important to talk to the young ones. You know...'train up a child in the way he should go and when he is old, he shall not depart from it...' paraphrased, of course.
My children and I drive for an hour each way at least twice a week. It is a great time to talk. My kids have memorized the first 8 articles of faith and they know what they mean too- not because they're like insanely genious (smart, though) kids, but because of the repetition. I doubt they'll ever forget those.
We talk about how we don't drink coffee and tea and that we dont' smoke, and what we can drink instead, like cocoa and milk and whatnot. They know about the word of wisdom.
I don't know about you, but our family prayers are short. scripture study is a page a day. Family home evening is often a fight. However, my children know that it happens. I am not sure they ever hear a word I say to them during these times. I know they know who Nephi is, and about Laman and Lemuel. But I don't know if they know any others. The point is, it's a habbit. It is something that is regular to them and I'm showing them that it is important to Me because I am doing it. I insist on it. And when I don't, they pick up the slack. It's wonderful. And it gives them something to build on when they're older.
I also pray daily taht I'm doing okay. that they will turn out okay- that all the television i let them watch won't rot their brains and all the yelling or lecturing I do won't make them need therapy. LOL. I think that's the point. We really can't do it all alone.