The human mind doesn't like empty spaces. Ask someone to articulate a hypothetical space in which there is nothing (really), and you won't get a good answer. We can't properly conceive a true void; the closest we can get is to visualize a space without air that is black.
The human mind needs content. Fortunately, this is the way God created it, but it means that we will always seek out content to give ourselves meaning. On a simple level, we love to ingest information. On a higher level, we adopt values and beliefs. We look at the world and interpret it, Christians by the revelation of the gospel, others by their observations of the natural world or the traditions they have received from their cultures. Where there is a question, humans want an answer. Where there is a void, we fill it. But with what?
Both grownups and children desire fullness. For adults, our voids are often of loneliness or disillusionment, and so we turn to gossip, pornography, an illicit relationship, or another worldview. We fill ourselves with what we think will provide satisfactory content to our empty spaces. Our children do the same -- but usually not until the late high school years and college. All through their growing-up years, they are subconsciously deciding what is meaningful and what is not, what is beautiful and what is distasteful to them. Once they get a measure of independence, they either accept or reject the content they've been given. And -- here's the rub -- they finally make those decisions based on what has given them the most joy.
Our children are always famished. So as parents or educators in a classical school, what are we feeding them? Stale bread and tepid water? Of course they will want more, and they will want what's forbidden. But if we serve up feasts, good and often, and with plenty of laughter, why would they want to turn anywhere else? Scripture, stories, art, music, crafts, projects, biographies, myths and legends, hymns and psalms, good food and dancing (yes), star-gazing, mathematical puzzles, discipline, joyful standards, the creeds of the faith, and a family unified -- serve these up (little by little, day by day, always-and-ever upward), and there will be no voids your children need to fill. But when those empty spaces falsely demand attention, your children will know where to turn. They serve a faithful God.