The aged leader told parents to teach their children who God is, so both child and parent would know and not forget.
Here is what Moses said to the children of Israel while they were still in the wilderness:
Hear, O Israel: The Lord our God, the Lord is one. You shall love the Lord your God with all your heart and with all your soul and with all your strength. And these words which I command you today shall be in your heart.
You shall teach them to your children, and shall talk of them when you sit in your house, when you walk by the way, when you lie down, and when you rise up. You shall bind them as a sign on your hand and they shall be as frontlets between your eyes.
You shall write them on your doorposts of your house and on your gates.
... lest you forget the Lord who brought you out of the land of Egypt, from the house of bondage(Deut 6:4-9, 12).
That old time simple instruction to teach them diligently remains relevant today.