"Sins are like grapes; they come in bunches. This explains two things that often mystify parents or teachers, but allow me to explain.
Often a child gets into a blue funk, bad attitude, the works. Demeanor surly, nothing helps, you know the drill. This can be seen most clearly in little children, who do not yet know how to disguise the condition of their souls. They have not yet matured to the level of the adult hypocrite, who approaches such things a little differently. Then, the child commits some clear infraction, and there is some appropriate discipline, and as if by magic, theentire mess is cleared up. The sin that was disciplined was simply the representative sin -- sort of a covenant head. And when it was cleansed, there was also a cascading cleansing everywhere else. The air is completely cleared.
And this phenomenon explains the second mystery, usually manifested with older children. This occurs when the sinning child is old enough to know about this cascading effect, and is serious about resisting it. When someone has got a backlog of unconfessed sin, true confession of just one sin is often like breaching the dam. The child knows that confession of other sins will follow, and if the cost of confessing those sins is too high, then they will do all in their power to avoid confessing the obvious one -- the one that would breach the dam.
As I said, this is far morely likely with older kids, and when there has been time and opportunity to build some sort of a double life. Say that a child is caught in something, open and shut, nothing ambiguous about it, and yet he stubbornly refuses to deal with it. This is not because extraordindary stubbornness is being embraced for its own sake. In this scenario it is not because of the "humbling" that will occur if he admits, say, that he took five dollars from his brother's dresser. It is because he (and he alone) knows that he has been stealing a lot more than that for years, or that he is deeply involved in pornography, or that he is engaged in homosexual behavior with a teacher at school. If he gives way at this point, the one sin everyone can see, then all hell will break loose. He knows the true costs of this confrontation, and nobody else does. Because of this, and because the human heart is a slippery devil, someone in this position can actually come to believe that he is sacrificing for others by hiding his sin -- that he is protecting the reputation of his family, for example. He is willing to suffer secret torments so that, for example, his father will not have to step down as an elder in the church.
If parents or teachers suspect that something like this is going on, the one thing they should not do is to start speculating, or asserting, or making baseless accusations. I believe that I have mentioned before that one of the verses I memorized very early on as a youngster was Num. 32:23 -- "be sure your sin will find you out." This was not because of spiritual industry at a young age, but rather because my mom quoted it all the time. If parents know this truth, and believe it, and if they understand that they have the authority to ask God to bring hidden things to light, then they can pray with assurance. "God, if there is anything here that we need to know as parents, but which we do not know, we ask You in Jesus' name to reveal it to us." That is a prayer that is in line with Scripture, and within the will of God. The hidden things will be brought to light, and the parents will then be dealing with the real issue."