Limit the number of characters. Too many characters confuse kids. They need to know who they are rooting for. Kids relate to conflict. Create a situation, the more impossible the better, then solve it, without adult intervention.
Kids have to know that they can solve their own problems.
Utilize descriptive words that beguile the senses. The more kids can see, smell, and hear, the better they will appreciate the story. Your main character must be one that most kids will identify with. Jennifer stuttered angrily. Your story may contain a morale, but do not make the mistake of preaching.