In our culture we have a belief that good parents will always produce successful children. We know that good training, influence and life examples are very important to aim the child in the right direction from an early age. We quote old adages like "As the twig is bent so grows the tree." So when a child makes poor life choices we parents tend to blame ourselves. And others secretly or sometimes not so secretly blame us as well.
However, there is a long time argument among philosophers and psychologists about which is most influential, nurture or nature? This argument inadvertently gives credit to the fact that God gave each human the right to choose. Yes, God is Almighty and in full control of all issues of the world outcome but within that framework He still gives us the right to choose and suffer the consequences or receive the rewards as a result. He put the Tree of the Knowledge of Good and Evil in the garden of Eden so that Adam and Eve actually had a choice they could make. The choice is always "Will I love and trust and obey God or will I be my own authority and take things into my own hands?" God was the best of all parents yet His children chose wrongly and effected the rest of the generations of humans to this day.
A child's wrong choices can bring a lot of heartache to the rest of the family. Yes, all parents make mistakes and wrong choices themselves as they raise their child. This needs to be admitted to the child and forgiveness asked for but the child's choice of how they respond even to the parents' mistakes is still their responsibility. After asking forgiveness of any wrong done be sure to affirm strongly your love and belief in what the child was created to be. Then shut up. They are an adult and not under your authority any longer. They would be wise to listen to your counsel but are not obligated to do so.
Now comes your hardest and longest lesson in life. You must yield your child fully into God's hands and begin a warfare in the Heavenlies every day on your knees. Collect scripture promises and pray them for your child. Stand in the Name and Blood of the Lord Jesus against all Principalities and Powers attacking your child. Claim a hedge of thorns around your child to drive them into the right way and drive wrong influences away from them.
My favorite verse is II Timothy 1:12"... He is able to keep that which I have committed unto Him against that day." Another translation says, "And I am sure He is able to keep safe what I have trusted to Him."
Have you done your part? Have you admitted any wrong doing or mistakes of your own? Have you affirmed your love and belief in your child? then commit them to Jesus and fight in the Heavenlies. Hold onto the promises. God is at work. Rest in that.