I learned how to program when I was 10 in exactly the way you taught your son. My dad used the GW-Basic interpreter that came with our AT&T PC6300, and we wrote a game where the computer asked you a question, and you had to answer A/B/C. The big advantage to syntax in GW-Basic was that you didn't have multi-line statements. You might want to try something similar. Java, with it's curly braces, might be a little tough.
Example code:
10 PRINT "What color is Big Bird?"
20 PRINT "A. Blue"
30 PRINT "B. Green"
40 PRINT "C. Yellow"
50 INPUT$ ANSWER$
60 IF ANSWER$ = "C" THEN PRINT "Good Job!" ELSE PRINT "Oops, wrong answer!"
I spent hours upon hours using various permutations of that syntax and writing my own "games". And it made me want to learn more... might help.