re: so my son finished 'learn.code.org' in one afternoon

Introduce him to the following two things (in that order)

1) Scratch (scratch.mit.edu)

Good resource websites:
Learnscratch: LINK /
Scratch Workshop from MIT+Harvard - LINK
Scratched: LINK
Gatech: LINK
Other: LINK
Free Book - LINK
Other: LINK
Other:LINK
Virtual Piano Demo: LINK
Good 16 Part Scratch course from Hurvey Mudd LINK




2) App Inventor (appinventor.mit.edu)

Free book - LINK
MIT's webiste for tutorials: LINK
Gatech: LINK
Free workshop - LINK

You might want to introduce him to Scratch first for a month and then let him work on App Inventor only when he has finished exploring all options.

After that, you might consider buying a Lego Mindstorms EV3 (~$400)