Erm, I assume you do want books that would be more likely to make the kids want to read more, and not ones that would turn them off completely?
When my son was in the 5th. grade, he absolutely loved "My Side of the Mountain", by Jean Craighead George. Here's part of the summary from Amazon: Every kid thinks about running away at one point or another; few get farther than the end of the block. Young Sam Gribley gets to the end of the block and keeps going--all the way to the Catskill Mountains of upstate New York. There he sets up house in a huge hollowed-out tree, with a falcon and a weasel for companions and his wits as his tool for survival. In a spellbinding, touching, funny account, Sam learns to live off the land, and grows up a little in the process.
For the girl: "Ellen Tebbitts", by Beverly Cleary. This was the first book I ever read that seemed as though what was in it really could happen. Any of the Ramona books, too.
Personal note--I will never, ever understand or agree with letting the age group The Lorax was designed for--4 to 8--read it. Ever. There will be PLENTY of time, later, for them to learn that there are bad things in the world. Let the ones they encounter personally (a classmate taking something of theirs, etc.) be enough, until then. They're busy enough trying to figure out how to operate in their immediate environment without worrying about the rest of the world. All of this aside from the fact that they're too young to handle this kind of anxiety; you wouldn't tell them every agonizing detail of Grandpa's cancer, would you?
