It seems that today we are reaping the whirlwind, having sown the wind with seeds of human philosophy. Wise parents help children understand Him, and love Him. The simple answer is because God said so. Beyond that, it's completely reasonable. Parents have the welfare of their child at heart like nobody else, including teachers, public officials, police officers, or others.
Parents have the authority of love.
Life is filled with opportunities to talk about God, about His creation, about His will, and about how we relate to Him. There's not a moment, nor an activity, nor an event that is not connected to God in some way, and wise parents help children understand Him, and love Him. There is no better foundation for life than love for God. Children ultimately become responsible for their own actions. That's what maturity and age are all about.