Children's fantasy is children's literature with fantasy elements: fantasy intended for young readers. It may also mean fantasy read by children, regardless of the intended audience.
Illustration from first edition of The Wonderful Wizard of Oz
Fantasy is a genre of speculative fiction involving magical elements, typically set in a fantasy world and usually inspired by mythology or folklore. The term "fantasy" can also be used to describe a "work of this genre", usually literary.
The Fairy of the Dawn in The Violet Fairy Book (1906)
Skeleton Fantasy Show (骷髏幻戲圖) by Li Song (1190–1264)
Another illustration from The Violet Fairy Book (1906)
Illustration from 1920 edition of George MacDonald's novel The Princess and the Goblin