I've read that most young people cease church participation because their questions (their quite reasonable questions) about faith, life and everything are not answered respectfully; that is, they are not answered, but side-lined with a 'just believe' response.
Not good, and not part of the tradition of inquiry that has marked Christian theology from the get go [I think of Peter writing about Paul, and Paul's discussion with Peter].
Answering questions has to start in Sunday School, and be continued through teen age years.
Children need to be taught both the Bible and theology: how to question, how to extract belief from the Bible and reason to their own experience.
In my SS experience, long ago as it was, I don't recall this happening, although some teachers did invite 'life questions' as I grew older.
One approach might be a modernised catechism as a structure for this part of training the young. For example, talking about who God is, why we believe in him and how we reason about belief and question both it and life...rich pickings for all ages, properly structured.
Even working through the Apostles Creed as a theological framework would be helpful, I think. Not just learn and recite, but study and think about from the Bible.
Another angle would be to look at God's self-defining actions in history, starting with the creation, through the patriarchs to the rescue of Israel to the resurrection as the first step in helping children to develop a rigorous doctrine of God (without using those terms, of course).