Choose Your Topic
What to write about? The best magazine pieces (and books) are particular stories that open out into larger questions or fundamentals. Start with what kids are curious about, and questions that they have. Ignore topics that you (or other grownups) think kids “ought to know.” Instead, follow what kids WONDER about and find cool. Or that they might think is cool if only they knew about it. (Octopuses have blue blood! Why?)
Leave the surveys of general knowledge for textbooks and encyclopedias. Instead, write the odd stories that will inspire kids to go to an encyclopedia to learn more. And that will captivate other kids on the playground when they retell it.
So, instead of “diseases are caused by microorganisms” (an encyclopedia entry), try “In 1854 a clever doctor figured out what was killing Londoners--it was a pump." You can explain all about microbes along the way. But it’s a story, not a lump of fact.
Channel your inner kid: what would your 8 year old self want to read, under the desk? OK, write about that. (I will understand if it's superheroes. But pitch those to Spider.)