From personal experience, I strongly disagree with the negative comments saying Forth isn't suitable for teaching children.

"Starting Forth" by Leo Brodie was the first programming book I ever read when I was about 6 or 7 years old, after my dad brought it home from work (where they used Forth). To me, the language felt very intuitive and easy to grasp. And Brodie's illustrations helped a lot with visualizing how it all worked.