Each story has a moral. Most of the writers end their story with a moral in order to make them more readable and interesting. It is often said that a story without a moral is worthless. Most of us read stories to know the moral which it has for us as a reader. All stories have positive moral and their aim is to teach something new to the reader. Which is the last story which you have read? What was the moral of that story? Do you like to read stories ending with a moral?

In simple words "toh batao bachchon, iss kahani se tumne kya seekha?" ;)

I think putting a question is a better way to let the kids know what a moral is - let them get back with answers, and sometimes those answers are so genuine and creative that you may reconsider your definition of moral :)