You can talk UP to children in your own books:
Ask Open Ended Questions
Open-Ended questions are questions that require a detailed response. For example, instead of asking, “Is it good to listen to your parents?” Ask “How does listening to your parents make them feel?” The two questions will guide your story in different directions. An open-ended question may also develop your story in more complex ways.
Let Your Characters Speak for Themselves
Get to know your characters well by developing them in your story. Make sure they do things they would do and say things they would say. Don't let adult characters control the kid characters or run the story.
Avoid Stereotypical Labels
Children are changeable, as are adults. As such, there is no need to limit them. A part of talking UP to children is to recognize that they grow and help them recognize it too.
Show, Don't Tell
If you have to share a message, don't tell your audience outright. Show them by example in the story you write and in the characters’ actions.
Get Down to Their Level
Maurice Sendak was known to say, “I don't write for children. I write and someone says it's for children.”
I appreciate the sentiment, but it is not exactly appropriate. Kids are not dumb, they are not simple, but they are an audience with special interests. The way I see it is, you must become an honest consumer of children’s literature. That way, the subjects you are interested in will also interest your audience.