That's a problem. A big problem. Christianity is not a secret and is not something to blindly (and silently) put our faith in. Doing so only stifles the natural curiosity for answers that God created us with. But it doesn't stop there. As Dan Brown admits, it was this lack of transparency that led him away from religion and ultimately into writing stories that blaspheme who God is (and acquiring quite a following, as evidenced by the millions of copies his books sell).
Why do we shun these questions? My guess is because the answers are difficult and complicated, often with more questions left unanswered. But is that a good reason to not even attempt to answer them? What's more, is it worth it to avoid these questions with the risk that those asking them might seek answers from another source? The answer is a definitive NO. Giving God the opportunity to work in people's lives even through the mysteries we can only estimate on is not only increasing the odds for discipleship but it is what God asks of us (obedience and faith).
So we need to talk. We don't need to know the answers to every question but we need to be willing to investigate them biblically and listen to what scholars and experts who have studied these topics have to say (who have also been guided by God's explanations biblically). We need to give God a chance to grow in these young minds and hearts, at the very least so we can know for ourselves what God says about such important topics. Then we can decide if we want to trust God or our best science.