One biblical principle for leading your children to God is to teach them the Ten Commandments. Not to just have them in their memory, but to know what they mean both externally and spiritually. For instance, “You should not lie.” This includes telling a lie and keeping quiet when you could tell the truth.
Why expose your child’s lie? What does it matter–he’s only four! The commandments show us (even four year olds) our need of a Savior. The function of the moral law is to show us our sin (Romans 7). The way to salvation is to first realize God’s holiness in contrast with our own sinfulness. Then to see how my lies make me need a Savior. Even 0ne or two year olds can begin seeing both.