Psalms 111:10 “The fear of the LORD is the beginning of wisdom: a good understanding have all they that do his commandments: his praise endureth for ever.”
In order to teach children the fear of the Lord, we must first teach them who God is, and what his righteous commands for us are.
Who is this God that he should be feared? God is holy, and good, merciful and compassionate. He knows all and sees all, and is everywhere all the time. He is terrible, all powerful, righteous and just in judgment. He is the God of the Old Testament. The same now as He ever was- He does not change.
Only when they know who He is, can they truly revere Him, and desire to be reconciled to him.
Through learning his laws they begin to see His holiness as a stark contrast to their own sin, and recognize their lost condition. And by learning of his righteous judgment of the wicked, they recognize His just judgment of their own sin and need for a Savior. In seeing God's great mercy and provision, they see His great love for man and recognize His great grace and unspeakable gift.
Galatians 3:24 “Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith.”
Proverbs 9:10 “The fear of the LORD is the beginning of wisdom: and the knowledge of the holy is understanding.”