Being Byzantine Catholic, I don’t know anything about CCD, but I’m guessing the problems leading to kids leaving after confirmation, start at home, not necessarily with CCD. [My children receive the sacraments of initiation (Baptism, Chrismation, and the Eucharist as infants). They attend catechism at our parish before Divine Liturgy, but it isn’t linked to a sacramental endpoint as CCD generally seems to be.]
So you can make CCD more fun, you can play games, etc., but if the parents aren’t setting the example at home daily, especially the father, then most of the time, there is only so much that an educational program can accomplish. The catechist only has an hour or so a week. The kids are being exposed to constant conflicting messages from many sources - T.V., internet, phones, teachers at school, peers, etc. That hour is probably going to get lost in the noise if there isn’t a strong example set at home.
In general, the families I know, Byzantine or Roman Catholic, where the majority of their children have continued to live a life focussed on Christ, are the ones that have made daily prayer as a family a priority, and that do their best to instruct their children in the faith at home, either as discussions at dinner or at other times. The families I know where most of the children left the church are ones where the parents have not been particularly involved on a daily basis. Sure, they made it to Mass most Sundays, but that was about it. (These are my observations.)
I’ve heard from a few Roman Catholic, “The family that prays the Rosary together, stays together.” We don’t pray the Rosary because it isn’t part of our tradition, but we pray together almost every morning and evening as a family, five to ten minutes. The habit of daily prayer has been long established. This is the most important daily witness to the faith we give them: prayer, turning ourselves to God to glorify Him, to ask forgiveness and offer penance, etc. The children know that their parents love and fear the Lord. They know that their parents want to go to heaven and that they fear hell.
But it doesn’t end with parents praying with the children daily, but their parents, must teach them, not as a supporting role to their catechism class (or CCD), but as their primary teachers of the faith. You mention the failure to teach about sin in CCD when you were enrolled. Parents need to be teaching their children about sin both by example in trying to live a Christian life, by going to confession and by encouraging their kids to go, and finally by instruction. (There are lots of books parents can use to learn the faith if they feel like they don’t know enough.) I am teaching my children, with lots of discussion, about living a life in Christ. It takes time, it takes recognizing that it is more important than watching more T.V., YouTube videos, reading novels, playing Angry Birds, etc. Then it takes doing something, which I know is even harder. (There are days that mindlessly watching T.V. sounds better and sometimes that even wins out because exhaustion wins.)
I wouldn’t necessarily look for teachers who are “qualified teachers in theology”, but someone who knows their faith and who lives a life of prayer. Someone who is trying to live a life in Christ. People followed monks into the desert not because they were “qualified theologians”, but they knew their faith and they lived a life of prayer; they lived holy lives. (Read some of the Desert Fathers. By our standards today, they are not theologians, but even now, their sayings and writing are very edifying to say the least.) Someone who has studied theology, but doesn’t pray or leads a life on the fringes of the Church, living in a sinful state in opposition to church teachings, is not a person I would trust to be involved in the education of my children no matter how well versed they are in theology.
In short, to answer the question about how to slow down the attrition of kids, in my opinion it probably all gets down to parents. I don’t know if there is anything that can be done in a CCD program to fix that.
Christ is Risen!