I am not a normal dad. Normal dads don't read Jonathan Edwards to their children the day they are born as they sit with them in the hospital. I guess that is one of the down sides of having a pastor as your dad, but from the time our children were born, I have read to them. And not just children's books, I have read adult books to them. I have read through most of the Chronicles of Narnia (among other things) with our oldest and the reason for this is simple. Studies have shown that reading to our children from a young age helps their development. They speak better and understand better through exposure to language. They begin to appreciate reading from a young age which, if it sticks and reading is a joy, results in a love of reading and exponentially increases their ability to learn and understand the world around them throughout their lives.
Not only have I read to my children, but my wife and I have never spoken "baby talk" to them. We have used adult vocabulary from the time they were born and as they grow, we explain those words we use that they don't understand. Vocabulary and language build culture and so, we have endeavored to instill in our children a vocabulary that shapes them. When they ask for something and the answer is no, instead of just saying "no", we say "no thank you". When they are given instructions we say "go pick up your toys please". When they respond correctly or when they do something considerate, we say "thank you". We have done this since they were born because, not only does this increase their vocabulary and ability to communicate effectively, but it creates a culture of civility and mutual respect in our home. So we have never treated them as though because they are young, they are stupid. The fact is they aren't and they are taking in everything they see and hear and that is forming, from the time they are born, their view of the world around them and shaping them as human beings. Let me give you an example of how profound this is.
Recently, I saw a teaching video of Paul Tripp called "Getting At The Heart Of Parenting" (you can find it here). In the session I watched, Tripp made a profound observation that shows how much our children are shaped by what they hear. He said that a small child that is learning to talk might come to a parent and say something like "I goed to the park with Mama". The parent would then correct the child and say "no, you went to the park with Mama". What has happened is something incredibly deep and insightful... your child, without taking any classes and without you intentionally telling them anything has made an amazing connection. They have observed that in English, many times when we say something in the past tense, we add an "ed" at the end. Played, stayed, prayed, jumped, lifted, filmed... and so on. But English is a weird language and so we have other ways of using the past tense with certain words. Went, sent, sat, drank... and so on. Don't miss the point though. That child made an amazing connection through observation and exposure. Our children, from the time they are born, are taking in much more than we give them credit for.
So, from the time our children were born, we have regularly weaved (see... past tense) the gospel into their lives. We share it with them, we talk about it regularly. It is a major part of our process of discipline. We use words like sin and repentance. We talk about Jesus dying and faith. When our children disobey, we talk about how they didn't trust Mama or Papa and how they need to trust us and more importantly, they need to trust Jesus. We talk about how they have sinned against us, but Mama and Papa sin too and all our sin is against God, but he forgives sin when we trust in Jesus. We read The Gospel Story Bible (available here and a version for younger children here) and talk about the pictures and the story. We repent to our children when we are wrong and ask their forgiveness telling them about how Jesus forgives us. The gospel is a massive part of the culture in our home.
Now, you might be reading this and thinking "well that sounds spiritual but studies have shown that children cannot understand complex ideas like that at such a young age. They are unable to comprehend those ideas. You are just wasting your time". I will admit, if salvation was merely about understanding propositional truths and mental ascent, this would be correct, but what the Bible says about salvation fundamentally compels me to share it with them. The gospel is called foolishness to those who are perishing (1 Cor 1:18). Unless something supernatural happens (the new birth) no one, no matter how old or intellectually capable they are, can even see the Kingdom of heaven (John 3:3). In fact Jesus says that human ability and wisdom doesn't help when it comes to salvation (John 9:39) and this is affirmed by Paul (Romans 9:16). All of God's sheep hear his voice and come to him (John 10:27-30). Notice that the emphasis is not on their ability but on God's action. You don't become a sheep by hearing his voice. You hear his voice because you are one of his sheep. In fact, Paul didn't provide a complex historical and logically convincing argument for Christ when he went to Corinth. He came knowing nothing but Christ and him crucified so that faith would rest on God's power (1 Cor 2:1-5). Faith itself is from God (1 Tim 1:13-14; Romans 12:3; Phil 1:29).
This faith comes by hearing the gospel (Romans 10:17) and saving faith is God removing blinders of the heart through the proclamation of the gospel and showing the glory of Christ in our hearts (2 Cor 4:4-6) which means that faith isn't a result of our effort. It is a sovereign work, a miracle of God, in which he changes our hearts, opens our spiritual eyes, and in that, we see Christ, treasure Christ and desire Christ which causes a response of repenting and trusting in him. It is the heart's cry for the object of it's greatest longing and satisfaction in Christ. No mere mental ascent can produce that. The Spirit has to produce that, and he works through the gospel being proclaimed. So, my children's greatest need is for a new heart which God has to give, and he gives this new heart sovereignly through the means of preaching the gospel such that no one can claim any credit for their salvation through their own intellectual aptitude or ability to rightly reason through the gospel. Therefore, the ability to comprehend complex ideas has no bearing whatsoever on saving faith. If that were the case, millions of mentally handicapped people around the world could never be saved. As Jesus said, "with man it [that is salvation] is impossible, but with God all things are possible (Matthew 19:26). I take that to mean that with God, the salvation of my children is possible at any age by him working through ordinary faithfulness of Christian parents in taking every opportunity, at every age, to share the gospel with their children. Or put another way, if God could regenerate (save) me as a spiritually dead sinner, and give me a new heart that sees the beauty of Christ in the gospel and desires him above all else through his word, he can do it with my child because we are in the exact same spiritual condition apart from Christ and God provides the cure to that condition as a sovereign act of grace.
So parents, preach the gospel to your children. They are never too young for the gospel. They are never without need for the gospel. Find ways to weave the gospel into everyday conversations. Incorporate the gospel into how you discipline. Talk about the gospel regularly. Share your need for the gospel and how Christ has saved you. Use the language of the bible in your home. Demonstrate a love for the gospel. Don't underestimate the power of the gospel. Show them the beauty of Christ in the gospel. Demonstrate grace and use that to point them to God's grace in the gospel. Pray that God would change the heart of your child through ordinary gospel faithfulness in your home and as you do, watch how God uses you as an instrument of grace in the lives of your children.