Programming for kids. Any suggestions?

[fermilevel@aol.com (FermiLevel)]

My son loves to write HyperCard scripts on both the GS and Mac.  He has
read the HyperTalk manuals cover-to-cover and knows just about every trick
in the book.  Now he wants to move to something more powerful, but he's
only 7 years old.  I want to encourage him to move to other things, but I
don't want to get him into something too complex that will turn him off. 
Does anyone have any suggestions?  Whatever he does, I would like it it be
useful on both the GS and Mac if possible.  Thanks for your suggestions. 
BTW:  he thinks LOGO "stinks", and also knows SimpleScript for
HyperStudio, so please don't suggest these.