first meet with the DRE and find out if the parish or diocese has a required curriculum and follow it. This is not the time to DIY, because the Confirmation II catechists will expect the children to have receive the required basics before they come to the sacramental class.
What should be taught for the first time (if they have not been to RE since first communion) is Divine Revelation and how to use, read and pray with the Bible, the basics of Salvation History, grace and redemption, the sacramental economy and how to participate at Mass, review of confession, elements of the Creed, and depending on when it is covered in your parish program, moral life in Christ. Christian prayer and spirituality is woven throughout the program.
when you find out the demographics of your class, and the framework the parish already has set up, come on back for more ideas.