How do I keep this from turning into homework?

Four things, and the last one is the hardest.

Do not quiz. The moment a child suspects a right answer is being fished for, the honest answers stop. Do not schedule it, because a weekly slot converts curiosity into obligation faster than almost anything else. Do not hold the activity back as a reward, which turns the idea into a chore the crayon is paying for.

And do not summarize the point at the end. The urge to land the moral is overwhelming and it undoes the work. They either got something or they did not, and the summary adds nothing either way.