Answer
The definition of indoctrination is "instruction in a body of doctrine or principles; the instillation of a partisan or ideological point of view." Indoctrination is seen as the act of imparting facts as truth without imparting the ability to critically consider those facts. In this way, we all indoctrinate children. We present clothes for wearing, beds for sleeping, and toys for playing. Every society is built on a foundation of principles that allows its citizens to easily relate to each other and work together for common goals. Christian parents are no different. They, like any other parent, often enact arbitrary rules to ensure peace or convenience. Christian parents also indoctrinate their children in Christianity for three specific reasons.
They believe Christianity is the truth. Imparting truth should be the goal of any parent. To do otherwise is at best laziness and at worst abuse. Christian parents indoctrinate their children in Christianity because they believe it is true. First Corinthians 2:12-13 says, "Now we have received not the spirit of the world, but the Spirit who is from God, that we might understand the things freely given us by God. And we impart this in words not taught by human wisdom but taught by the Spirit, interpreting spiritual truths to those who are spiritual." By passing on truth, parents show their love and respect for their children.
They believe children will benefit from understanding Christianity. If Christianity is true, then learning about it will be beneficial. Receiving training in God, humanity, sin, and salvation becomes absolutely vital. The Scriptures provide this training. Second Timothy 3:16-17 says, "All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness, that the man of God may be competent, equipped for every good work." There should be a relationship between the child and Christianity—the child learns, accepts, and lives out his beliefs. If the relationship breaks down at any part, indoctrination becomes vain speculation.
They believe they are living out their beliefs. Just as the child must be actively engaged in Christianity in order to benefit, the parents must also. This includes ensuring their children understand their faith. Deuteronomy 6:7-9 says, "And these words that I command you today shall be on your heart. You shall teach them diligently to your children, and shall talk of them when you sit in your house, and when you walk by the way, and when you lie down, and when you rise. You shall bind them as a sign on your hand, and they shall be as frontlets between your eyes. You shall write them on the doorposts of your house and on your gates." If the parents believe and follow Christianity, then they believe and follow the Scriptures' admonition to pass on those beliefs.
Christian parents indoctrinate their children in Christianity because they believe Christianity is true and they believe that understanding Christianity will benefit their children. In a world of turmoil and violence, Christian parents hold fast to the promise Scripture gives them: "Train up a child in the way he should go; even when he is old he will not depart from it" (Proverbs 22:6). Critical thinking has a role in becoming a Christ-follower; every child must make a personal decision to follow Christ. It is the parents' responsibility to explain the importance of that choice. Indoctrination in the Scriptures is the most effective way to do this.
