But ながいながいペンギンの話 (Nagai nagai pengin no hanashi, "A long, long penguin story") by いぬいとみこ (INUI Tomiko) is an easy book to read. The cover of my edition says that it's suitable from the third or fourth year of primary school (age eight or nine). INUI Tomiko (1924-2002) was a editor of children's books when she wrote it. It was published first in installments in a doujinshi (an amateur literary magazine) from 1954 to 1956, and came out in book form in 1957.
INUI explains at the start that this is not the story of a long, long penguin, but a long, long story about Ruru and Kiki, two Adelie penguin children growing up in the Antarctic. According to the page on the book on the website of the (now disbanded) International Institute for Children's Literature, Osaka, shorter stories were typical for younger children at this age. It is still not a very long book (177 pages), and the story is divided into three self contained parts, all focusing on the more adventurous of the two brothers, Ruru.
|Adelie penguins (from Wikimedia Commons: Hans Grobe, Creative Commons 3.0)|