This advice is given to writers all the time: Study publisher catalogs to find out what they publish to see if your manuscript is a good fit. Quite honestly, I have never found such study to be a practice worth my time (and that's even before I had an agent to make submissions on my behalf).
Perhaps if I were a nonfiction writer there would be some value in studying catalogs. I might find out that Publisher X has an animal series that lacks the book on wombats I'm dying to write and that I'm sure they'll want. But how does studying catalogs help the fiction writer? All you really need to know is if Publisher X publishes fiction for the age group and in the genre(s) you write. That information is readily available in the marketing section of writer magazines and online, and in reference books like Children's Writers and Illustrators Market Guide.
The truth is, the big publishers ALL publish the same kinds of things. And knowing that Publisher X has two other series of fiction chapter books about princesses doesn't tell you a thing. They might not want to publish a third series of princess books, but then again, they might. The only way you'll know for sure is to query or send them your manuscript.
If you've got an alternative viewpoint on this issue, I'd love to hear it!