Remember, if you help another person sin, you are entering into their sin.
If you cooperate with sin, you are sinning. You are part of the cause of the other person or person's sinning. Remember that silence is consent. This is hard for youth to grasp.
Help your children learn this. Let them follow the example of St. Thomas More in all things. He formed his conscience according to the Scriptures and the Teaching Magisterium of the Church. Formation begins very young.