what is the assumptions, ideologies , and discourses about children and childhood reflected in different litery texts
I would play safe on this one with suggesting that there are many assumptions and understandings about children within literature. I think that one fundamental assumption is that children's literature can be a vehicle a transformative vision of reality. Children's literature can be liberating because it speaks to the promises and possibilities of childhood and maturation from that premise. It helps to bring out the better aspects of what it means to be a child and seeks to broaden the moral and creative imagination of the reader, presumably children and parents. For example, when reading literature intended for children, "Charlotte's Web" or "Stuart Little" or "Little Women" or "The Wizard of Oz," there is a quality in each that identifies what reality is and uses the medium of literature as a vehicle to reflect what it can be. Reality, as constructed by the authors and publishers of children's literature, is dynamic, capable of individual attempts at change and not something that is deadening. It is not the wilted flower, but rather the lively grove of beauty and wonderment. I don't see this as exaggerated prose. I think you can apply this to any of the "100 Best Books for Kids" as selected by teachers and parents.
I think the main assumption about children (in most literature) is that they are innocent, naive, and as a result of inexperience - ignorant. Of course this most often isn't true (not even in real life). It is an underlying assumption that sets the stage for so much situational irony in literature. Here are some quick examples:
Scout, in To Kill a Mockingbird - gives lessons to her Uncle Jack Finch in parenting and lessons to her teacher Miss Caroline Fisher in teaching. Both instances are considered situationally ironic because we are not to expect a child to know more than an adult - but in this case, she clearly has some sense of sitautional wisdom that Uncle Jack and Miss Caroline do not.
In The Scarlet Letter, the character with the best eye for the truth is of course, little Pearl. Again, it is situationally ironic for Hawthorne to use a small child (and the very product of sin no less) to be the one character who seems to be drawn by truth.
In Adventures of Huck Finn, Twain uses a young boy to portray everything that was laughably wrong with slavery and racism. Again, situational irony - that Huck, an uneducated trouble maker, is able to see a higher moral principle than the adults who try to teach him right from wrong.
In general, the underlying assumption/ideal of children being naive, innocent and ignorant is an opportunity to make a more profound statement of truth through their eyes and lips. It is even more embarrassing/impactful when a kid gets it (the moral truth), and we adults don't.