I used Forth to explain numbers in different radices to my grandson. Being able to interactively try things at the console was really helpful. It also helps to separate the internal number in the machine from how we display it, due to the different operators to print numbers as signed or unsigned. This is something that I have seen young programmers confuse.

I think another area where Forth can help young people is in understanding some low level details like memory addresses and reading and writing memory. It seems simpler than abstracting it to "pointers", more like assembler but interactive.