In "Doctrinal Discussion" Jason Lindahl writes:
“And when thy son asketh thee in time to come, saying, What mean the testimonies, and the statutes, and the judgments, which the LORD our God hath commanded you?” (Deut. 6:20). “And when thy son asketh thee”: The assumption is that your son will ask you. If your children do not notice that they are different from the rest of the world, then something is wrong. Jesus said of His disciples, “They are not of the world, even as I am not of the world” (John 17:16). If we are truly Jesus' disciples, our children will notice that we are different. The answer is not simply, “Because God said so.” That is the beginning of the answer, but notice: The children already know that. They know that these rules are what “the LORD our God hath commanded you.” But why did He command them? Why does He require these things of us? Why do we have to be different? They need to know, “Because God said so,” but that is not enough.
Source: Building Christian Relationships: Adult Teacher's Insights, page 62.