Why are there awards and prizes for children's literature?
There are many awards for children's literature. But as for the "reason," this type of writing must meet a high level of expectations. The writer must engage young minds, create interesting illustrations, and provide insight into the world in a way that is exciting and creative.
Perhaps the largest and most prestigious award for young children is the "Caldecott Prize." The Caldecott awarding committee considers "the artistic technique employed; pictorial interpretation of story; appropriateness of style of illustration to the story; delineation of plot, theme, characters, setting mood or information through the pictures; and recognition of a child audience."