At that age, the various books by Edgar Rice Burroughs would probably be appropriate - Tarzan, John Carter of Mars, some of his Venus books. The "science" is dated, but they were entertaining for a youngster. Likewise Tom Swift. (Unlike the current TV show, Tom back then was not a black homosexual.) I also read stuff like Wells' War of the Worlds as well as paperback reprints of the old "pulp" magazines like The Shadow and Doc Savage.
If you really want to read aloud, take a gander at the various African hunting books by the late Peter Hathaway Capstick - Death in the Long Grass, Death on the Dark Continent, Death in a Lonely Land, etc. These books are divided into chapters, well suited for a single reading aloud session. Any 11 year old would probably pay close attention to someone reading a chapter with a title like The Killer Baboons of Vlackfontein.