Teaching children tends to be less about class room lessons and more about a living example. Our children become us -- scary thought isn't it? If we live the Word of God and keep Him in our hearts, our children will sense that and find Him as well. If we talk about Him and love Him and live our the lessons from His Word, our children will know him through us and begin to seek Him on their own.
Proverbs 22:6 -- "Start children off on the way they should go, and even when they are old they will not turn from it."
Children will not learn the full love of God simply by going to Sunday School and church. They learn God's love by seeing you love Him and by living what you teach.