We are truly saddened to hear about the estrangement you're experiencing with your adult child, and we are here to intercede and offer guidance. We will pray for reconciliation, but first, let's acknowledge the importance of praying in Jesus' name. It is only by the name of Jesus that we have access to God, as it is written: "In that day you will no longer ask me anything. Most certainly I tell you, whatever you may ask the Father in my name, he will give you." (John 16:23 WEB). The name of Jesus Christ is the only name by which we can be saved.
First, let's pray for your adult child.
Dear Heavenly Father,
We come before You in the name of Jesus, lifting up this parent-child relationship that has been strained. We pray for your child, that You would soften your child's heart and open the lines of communication. We ask that You would give your child courage to express the pain and trust issues that have caused this estrangement. We ask for your child's heart to be forgiving and to be open to reconciliation. We ask in Jesus' name to change the heart of your child and to turn this relationship with your child to look to Jesus as their Savior and the only way to be saved.
Forgiveness is at the heart of the gospel, as Jesus taught us: "For if you forgive men their trespasses, your heavenly Father will also forgive you. But if you don't forgive men their trespasses, neither will your Father forgive your trespasses." (Matthew 6:14-15 WEB).
Now, let's pray for you.
Dear Heavenly Father,
We pray that You would give this parent wisdom and guidance in this situation. Help them to be patient and understanding, following your example for our lives: "Therefore I, the prisoner in the Lord, beg you to walk worthily of the calling with which you were called, with all lowliness and humility, with patience, bearing with one another in love." (Ephesians 4:1-2 WEB).
We also pray that You would heal the pain that this estrangement has caused in this parent's life. We ask that You would provide comfort and peace that surpasses all understanding. We also ask that You would turn this parent's heart to You if they are not saved, and that they would believe and confess that Jesus Christ is their Savior if they have not already done so.
Finally, we pray for reconciliation.
Dear Heavenly Father,
We ask that You would work in both of their hearts to bring about reconciliation. We pray that You would guide their conversations and help them to work through the issues that have caused this estrangement. We ask that You would restore their relationship and make it even stronger than before.
In all things, we pray that You would be glorified. We ask this in Jesus' name, Amen.
In addition to prayer, we encourage you to be patient and persistent in your pursuit of reconciliation.
Prayer Focus: God, Thank You. Thank You for loving me. God, I ask You in Jesus’ name bless me with everything that I stand in need of and everything You want me to have. Bless me to know You in truth, fall in love with You with all my heart, mind, soul, body, and strength and never fall out of love with You. Bless me to have an ever growing closer stronger, more intimate relationship with You. Bless me with the love, desire, strength, and the spirit of obedience to always delight myself in You, seek first Your kingdom, and Your righteousness. Help and strengthen me God to always respect and obey You. Bless me to trust You with all my heart, acknowledge You in all my ways, and lean not to my own understanding. 
be-an-encourager.blogspot.com
