Writing non-fiction for magazines is actually a terrific way to get your foot in the proverbial door to publication. And yet... I have found very few resources that focus on writing non-fiction for children. Information on writing for magazines is targeted to an adult audience; information about writing for children is usually geared toward fiction writers. What I'm trying to do is somewhere in between.
How then, to begin? Well, I've been diligent about reading my Children's Book Insider and SCBWI Bulletin when they come out (this is one of my resolutions for the year—to make use of the information while it's still fresh and relevant).
I've written several articles on topics that are listed under "current needs" for their magazines. And I have done my homework by (1) reading every last letter of the submissions guidelines and (2) checking out old copies of said magazines from the school library. The latter has helped a great deal in terms of writing style, and the former I somehow failed to do for one of my first submissions (either that, or Highlights changed their submission requirements after I submitted; I suspect it was my error and the form rejection was a nice stinging reminder to pay closer attention).
I must say that the Children's Book Insider and the SCBWI Bulletin are essential tools for the children's author. If you write for children (or want to), you need them. I recommend both, since publishers advertise information in one, but typically not in both, at least not at the same time.
How have you found writing opportunities?