Aim your fiction at a specific age group. According to Children's Fiction factor, most scary fiction is read by children between the ages of 8 and 12 years. However, bear in mind that there is quite a difference between an 8-year-old and a 12-year-old. Spend time with children of this age group, if possible, and familiarize yourself with what makes them tick and what they enjoy.
Develop your main character and spend time deciding whether you feel most comfortable with a boy or girl character. Children indulge a little in their naughty side by reading scary fiction because adults sometimes disapprove, so the main character should be basically a good person but should push the boundaries sometimes.
Decide on the level of fear you want to evoke. Ideally, you want to maintain the chill factor without really frightening the child. The secret is knowing where to pitch the fear. Many writers in this genre are experts at making the mundane suddenly turn into something frightening.
Avoid nasty things from happening to the main character or those close to him. Add several cliffhangers to hold the readers' interest, so that the children keep turning the page. Keep a moral thread running through the story; good should ultimately prevail. Avoid too much gore. Make your readers feel empowered by making your main character strong. Always end on a note of hope.