I Timothy 5:24-25
Some men's sins are open before hand, going before to judgment; and some men they follow after. Likewise also the good works of some are manifest before hand; and they that are otherwise cannot be hid.
One of the hardest lessons to learn as a child or adult, is why sometimes sin is not punished and why righteousness is not rewarded immediately. I'm pretty sure all of us has asked that at least once...a day. :D
Remember last time we were talking about fairness and favoritism? Sometimes we feel like God is playing favorites by not punishing someone or by rewarding someone else. But by having that kind of attitude, we are opening the door for our children to say the same things to us, and with more justice, for we as humans are much more partial than God.
I have been so encouraged lately about this from reading Psalm 73. I encourage you to read it for yourself and pray God will help you have His perspective on this issue.
The main key is we need to teach our children that justice and rewards will be handed out but we don't get to choose the time. It can be very obvious to us that some one is a liar and yet no one seems to be calling them on it. Rest knowing that God has a reason for allowing him or her to continue. If we can show them peace in our hearts with God's timing, they will feel the same.