What is that?
Children’s literature is
--Children's literature or juvenile literature includes stories, books, and poems that are enjoyed by children.
Modern children's literature is classified in two different ways: genre or the intended age of the reader.
voc:
juvenile(adj)形容詞[only before noun 僅用於名詞前]
especially law -connected with young people who are not yet adults 【法律】少年的
silly and typical of a child rather than an adult 幼稚的,年幼無知的
genre (n) [C]可數名詞
formal -a particular type of art, writing, music etc, which has certain characteristics that all examples of this type share
【正式】〔藝術、寫作、音樂等的〕類型,體裁
What is that for?
Stories and Poems for Extremely Intelligent Children of All Ages by Harold Bloom 
Why should I care?
凡是為兒童寫而又適合兒童欣賞的文學作品,才是「兒童文學」。
(a) picture books--a book for children with many pictures in it
(b) fairy tales--also fairy story [countable]
(c) nursery rhymes--[countable]
(d) Initiation:the process of officially introducing someone into a club or group, or of introducing a young person to adult life, often with a special ceremony:
Quest:[countable] literary
a long search for something that is difficult to find
Bildungsroman--教養小說; 教育小說(描述主角心理成長及道德教育的小說)
其實,這個定義最可取的地方,最能夠跟那個重要的「但書」相呼應的地方,就在「為兒童寫」這句話上。「為兒童寫」是創作的目標或者那部作品的基本的寫作意向,「適合兒童欣賞」是那效果。
兒童文學作品,可以寫兒童,也可以不寫兒童,「寫兒童」並不是兒童文學創作的「必要條件」。最明顯的例子是:兒童最喜愛的動物故事跟神話故事,那主角往往不是兒童。----林良《淺語的藝術》
103美國文學 (1)