I am a big fan of nonfiction picture books as a way to help Japanese language learners to take the next step after graded readers. Fiction picture books, folk tales, and books for the very young have vocabularies and grammar that native speaker children learn from their parents and grandparents, but nonnative speaking adults wouldn’t come across in their textbooks. Some folks are fine with it and figure it out, but others will be frustrated that they can’t understand something that a tiny tot can.
Nonfiction picture books are short – maybe 32 or 46 pages – and have plenty of illustrations to help with understanding the text.
I have a number of them in my READ Japanese collection, including biographies, history, social issues, etc.
Some, aimed at older Japanese kids are longer. The following series averages 80 pages. The reading age is just 小学生 but I would say that it would be really good for students in their 3rd or 4th year of Japanese – particularly students who are working on a project and want to read at least 1 book in Japanese.
At the moment I can’t remember if I have ordered these or not, so I am going to put the link in so I can come back to it.SDGs=Social Development Goals.
This set of 10 books covers a range of topics from poverty to pollution. It explains the issues in a story and then provides more information. The publisher is Kodansha, 2020-
For a list of the titles and ISBNs see ehonnavie here
Sample pages and an article about the series is here at Jiji.com.