O. Henry's "The Ransom of Red Chief" is one my kids loved when they were small. As they got older (they're now 12 and 16, and we still read out loud on occasion) I enjoyed bringing them some more sophisticated stories like Roald Dahl's "Parson's Pleasure." That is one of my favorite all-time short stories, but I enjoy all of Dahl's work. The stories about the rat catcher, read in sequence, are positively agonizing, they're so well-crafted.

I also agree about Mark Twain. Huckleberry Finn is one of the funniest and also most thought-provoking novels ever written.

SRS