When I was a little kid, there was no TV. My grandmother would read to me every day, several times a day. My favorite book was Sonny Elephant, except I hated the ending. I told my grandmother that I didn’t like that ending, and wonderful woman that she was she would pretend to be reading the book, but she would substitute an ending I liked better.
That experience is so valuable now that I’m a writer. Kids will tell you if they don’t like a story if you let them. All you have to do is ask. it doesn’t have to be a kids’ book either. In fact, they are a great resource for ealuating the plot of a novel. Just tell them the story. Do they want you to keep talking? If they are hungry for more, then you have enough action in your story, and if you can keep yourself from writing a bunch of boring description, you’ll probably have a winner. If they are bored, they will let you know, because unlike your adult friends they don’t worry about hurting your feelings, and you had better rewrite that plot.