Their flesh is weak. It is not just your criticism that weighs them down. Their own conscience is actively critiquing their performance. They feel badly when they don't live up to their own expectations. Parents have the maturity and the will power to give them the structure and the fortitude to do what they know they ought.
Children have the same inner struggle as adults.
They are a living soul created to glorify God. The need to walk in righteousness is innate in every human being, even children. The human soul cannot find peace unless living to glorify God. This means living benevolently, speaking kindly, and living sacrificially for the sake ofyour fellow man. Yet the flesh of the child stands in opposition to the law of the mind.