What do you do when they have heard it all before; your son or daughter seems to have all the right answers, but their life is opposite of how we know a Christian is to live?
How do you get through the heartache and the heartbreak of realizing that one of your children is not a part of God's family?
How much do you say to them about salvation? Do you cut them off for refusing to repent? These are but a few of the questions the parent of a prodigal child has. There are so many variables in situations I would not attempt to give a "one size fits all" response to them, but some things will be universal and I will outline them here.
Parent: you are responsible before God to present Christ to your child and to live a life that glorifies God. That is a life of honesty, integrity, service to others, and selflessness. You are responsible to live what you say you believe! If you have brought your children up in the reverence of the Lord, with a solid biblical foundation - that is all you can do. Ultimately, you are not responsible for what your child does with the Jesus question.
Parent, you are responsible to pray for your child. Wayward or not, prayer is always the right thing to do for others. Parents struggle knowing what to pray for though. It is hard to pray God would bless your child when he/she is living a life of wanton sin and rebellion. In such a case, prayer for repentance and conviction is in order, not a blessing! The best thing that could happen to a rebellious child is to be under the discipline of God. Pray that God would do whatever it takes to bring your child to the place where they cry out for the grace and mercy of God.
Praying for God to act in your child's life means you have to stay out of the way when He does! The hardest thing for parents is to stop protecting our children from things that hurt. In this case, some pain and hurting may be the very best thing for your child. Nothing makes us cry out for God like pain and suffering does. God is the master surgeon, He knows exactly what is needed to affect the heart.
Continue to evangelize your child. Even though they have heard the gospel many times and may even claim to believe, if their life's work is not directed biblically and lived with a desire to glorify God, they may not be saved.
Continue to love your child, and tell them so, often. Accept your child for who they are and don't expect them to act as though they are saved when they are not. Always speak the truth in love and remind them that God's mercy never fails.