I have always taken C.S. Lewis's approach to reading for children. Our children are free of all books in our house, although I have forbidden my son to read several rather violent science fiction books "until you are older." We have some rather unusual and remarkable books - of course, we don't have any real trash of the sort that dirty old men used to buy in the bookstores with paper over the windows. But, as my daughter sniffs, "Who would want to read THAT?" (world of scorn from critical reader.) Expose them to the really good stuff early, and they will make appropriate judgments on their own.