Your signature on this forum says a lot about you, and perhaps that is a place to start.
The first part of your signature says, JESUS I TRUST IN YOU! Share with the retreatants your answers to questions such as, Who is this Jesus to you? Why do you trust Him? How do you develop and maintain this loving, trusting relationship with Him? (This may be a way to introduce them to the idea of spending time each day in personal, intimate prayer, something which many young people have never experienced.)
The second part of your signature says, “Lord Jesus, Holy Mary, St. Joan of Arc, and all the angels and saints, Pray for me as I try to live my life as a child of God.” You could spend some time giving concrete examples of how you try to live your life as a child of God, and how your efforts to do so strengthen your relationship with Jesus.
Be sure to pray to the Holy Spirit to help you. Sometimes when I have to do some important spiritual writing, I like to do it in the presence of the Blessed Sacrament, either in our Adoration Chapel or near the tabernacle at church. The famous Archbishop Fulton Sheen did some of his best writing in the presence of the Blessed Sacrament.
God bless your efforts!