"Adults tend to forget - or perhaps never appreciated in the first place if lifelong non-readers themselves - what a vital part of the process rereading is for children. As adults, rereading seems like backtracking at best, self-indulgence at worst. Free time is such a scarce resource that we feel we should be using it only on new things.
But for children, rereading is absolutely necessary. The act of reading is itself still new. A lot of energy is still going into (not so) simple decoding of words and the assimilation of meaning. Only then do you get to enjoy the plot - to begin to get lost in the story. And only after you are familiar with the plot are you free to enjoy, mull over, break down and digest all the rest. The beauty of a book is that it remains the same for as long as you need it. It's like being able to ask a teacher or parent to repeat again and again some piece of information or point of fact you haven't understood with the absolute security of knowing that he/she will do so infinitely. You can't wear out a book's patience."
Lucy Mangan, Bookworm: A Memoir of Childhood Reading