I've been teaching 10 9-year-olds Kodu Game Lab this week in my home and they love it and are understanding the concepts of event oriented programming while creating computer games. We tried Small Basic but they are all just learning typing and that was a bit of a barrier. Kodu is extremely easy to learn and very fun for kids.
Disclaimer - I work for Microsoft, the creator of Kodu Game Lab and Small Basic.
Michael S. Scherotter