You may completely disagree, but have you considered offering them more adult fare? These are the ages that kids no longer want to be treated like kids. They want to be treated in a more mature manner, and that includes instruction for them. Teach them the faith. Don't sugar coat. And don't make it "about them" as counter-intuitive as that may sound. But the reality is, the world ISN'T "about them."
That is the world they must function in. So give them the knowledge they need to live out their faith. Not just a bunch of entertainment to keep them "happy" for an hour on Sunday morning.
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The Sunday School class my kids are in has 3 kids. Them (grades 7 and 10) and one other 10th grader. Smaller can be a good thing. Use it to your advantage to let them open up and discuss. It doesn't have to be "structured" so much as long as you are teaching them. My kids' class sits on sofas and they talk about all kinds of things. Usually, it starts out discussing the gospel reading for the week...
Personally, I think part of the reason so many youth leave the church is that they are taught (from an early age) that the deep issues of theology are beyond them and that they are only "worthy" of the fluffy stuff for discussion. It might be subtle, but that is the message they take away many times. Rather than teaching them about morals, teach them the faith. Rather than teach them law, teach them the reality of sin and what the answer to it is. It isn't "trying harder to be good". It is Christ. And every time they fail (and they will, as every one of us does) the answer is always Christ. Not to try harder, not to do better deeds, not ____. It's confess and be forgiven in Christ.
They need to know it is ok to fail. It is ok to make mistakes. It is okay to do wrong.... not because it is "good', but because they are forgiven. Lots of preaching (and Sunday School lessons) are about bettering ourselves. In my opinion, it shouldn't be. It should be about the reality of what the Gospel means for us. Forgiveness. Teach that to the youth. They need to hear it. Regularly. Just like adults do.