I love LEGO::RCX. The original programming environment is very object-like, you stick pre programmed modules together in a graphical interface thats simple and fun to use.
However, there are a couple of things missing: Variables, and flexibility.
But once your child gets to the point of wanting those things, there are other programming languages available for the RCX.
NQC (Not Quite C) is a great next step, and gets the programmer into using variables and counters. There are a couple of good books on the Mindstorms robots, and programming them in RCX, NQC and other languages.
Plus the Legos are still fun to play with. :-)
I just realized that this was my 100th writeup. Thanks perlmonks for being here! :-)
In reply to Re^3: How to introduce 8 year olds to (Perl) programming?