Now that Conrad Barski's Land of Lisp (see my review on Slashdot) has come out, I definitely think Common Lisp is the best language for kids (or anyone else) to start learning computer programming. Between Land of Lisp, David Touretzky's Common Lisp: A Gentle Introduction to Symbolic Computation (really great book for people new to programming, available for free) and The Little LISPer (3rd editio