Learn to Program, Second Edition (The Facets of Ruby Series)
I was really impressed with Ruby. I ran through the 20 minute tutorial and then started reading this book. The book is great! The author teaches children so he knows how to hold your attention. It's fun! I honestly have never in my life seen a better introduction to programming for kids or beginners. So, hopefully, the kids will enjoy learning Ruby this summer. I'm pretty sure my son will like the idea of programming an old style, text based adventure game. When they're done with that, I'll show them Perl.