While their hearts are far from me

Children are very astute observers of interpersonal dynamics. They recognize what is desired by authority figures, and can learn to 'play the game.' The child who is caught taking candy from the jar when she should not says a quick "Sorry!" though she does not mean it, because she knows that this is what is expected of her. She may even be able to feign sincerity, knowing that her parents will not be satisfied with a sassy "sorry."

As soon as a child is old enough to understand what is required of her, it is not too early to begin teaching the dangers of hypocrisy. The word of the LORD through Isaiah provides a great occasion for teaching:

Because this people draw near with their mouth
and honor me with their lips,
while their hearts are far from me,
and their fear of me is a commandment taught by men,
therefore, behold, I will again
do wonderful things with this people,
with wonder upon wonder;
and the wisdom of their wise men shall perish,
and the discernment of their discerning men shall be hidden. (Isaiah 29:13-14)

Even a young child can understand what it means to draw near to someone "with their mouth" while their heart is still far away. Their own experience of disobedience and feigned repentance connects with the behavior that is condemned. So we can impress upon our children that what God desires, and we desire, is not merely right words, but a right heart. For as God brought judgment on the people of Israel for their hypocrisy, because they honored Him with words while their hearts were yet estranged, so He will not endure our hypocrisy if we draw near to Him with words only, while our hearts are far from Him.

Learning this early, by the work of the Holy Spirit, will save children many, many pains.