Relax. Let me offer you a good place to start: take a look at the editorial calendars of potential markets. Editorial calendars are usually found on the guidelines page of a publishing company's website. Here you'll find a list of themes and the month and year in which those themes will be published. In some cases, editors have listed possible topics. Take for example the theme “Age of Exploration” as listed for Appleseeds Magazine. The editors state they’d be interested in seeing ship builders, sail makers, map makers, and explorers. Think of all of the possibilities just from this one theme!
When I glance at the editorial calendars from different magazines,I find that many of the themes are broad. For instance a couple of years ago, Appleseeds Magazine listed “horses” on the editorial calendar. You could write about a particular breed, horses in history, horses helping people, and so on. But the key to catching an editor's eye is to find a specific and a unique facet of the topic. In this case, I found a unique subject—a candy-loving Kentucky Derby horse. This unusual horse and his story impressed the editor and I was awarded a contract to write the piece.
An editorial calendar gives you ideas that you may not have thought of before. When you review the themes, think about a topic that interests you and has the potential to interest kids. Ponder how can you make this topic exceptional. Consider how you’d research the topic. Afterward, think about where you will submit such an article. You can pitch to the publication that has presented the theme. Or you can use the topic for a piece that can be submitted to a different magazine.
If you’re not quite ready to begin researching, writing, and submitting an article, simply keep a list of all of the topics for future reference. Check the editorial calendars throughout the year to see if any have been updated. Review your list and brainstorm other closely related topics. In time, you’ll never be short on ideas.