This idea started when the Bible lesson was the great commission from Matthew. The verse said Jesus and the eleven disciples went up the mountain. I asked them if anyone knew why there were only 11 not 12. No one knew. So I told them if they found the answer I would give them a candy bar.
The next week I had a different question.
Surprisingly, they enjoyed finding answers. In fact, one week I didn’t have one and they were disappointed. I think this is a good way to get them to open their Bible and become familiar with the stories and people.