I would recommend several things,<p>Squeak by Example[1], or better yet etoys[2]<p>How to design worlds, as already mentioned here<p>Alice[3], with something like [4].<p>Good old scratch from the logo tradition would also be cool[5].<p>[1] <a href="http://squeakbyexample.org/" rel="nofollow">http://squeakbyexample.org/</a><p>[2] <a href="http://www.squeakland.org/" rel="nofollow">http://www.squeakland.org/</a><p>[3] <a href="http://www.alice.org/" rel="nofollow">http://www.alice.org/</a><p>[4] <a href="http://www.aliceprogramming.net/" rel="nofollow">http://www.aliceprogramming.net/</a><p>[5] <a href="http://scratch.mit.edu/" rel="nofollow">http://scratch.mit.edu/</a><p>Check them all out and decide for yourself. All of them are very consistent and fun.