In writing for children, the first thing you must determine is the age of your audience. Are you writing for preschoolers? Are they 1-3? Are they 3-5? First through third graders? Fourth through six graders? You must mark your audience. Then, you must write to that audience. You cannot just write for children without targeting your work to a particular age. Most children’s publications are geared to a specific level: primary, junior, etc.
Then you must be totally in tune with the age level you are writing for. Know their likes and dislikes—use their language, but not words that are trendy and will be outdated in a year or two. And most of the time, you need to use words they are familiar with. Occasionally you can teach them a new word, but be sure to define it in context.
If you have children of your own or grandchildren, have them read what you write and critique it. If you don’t have children in your family the age you want to write for, find some children in your neighborhood, teach church school, or sponsor a youth group. Go to a playground or teen hangout—and listen!