[fn-mote]

> But whenever I show him "real" programming languages, he's like: I can do all of that with Scratch as well - without having to type all that stuff.

Dear Hacker:

Your son is already doing things kids four years older would be amazed by.

Let him come to "real" programming on his own.

Heck, show him Snap and let him write programs with call/cc in "Scratch". Maybe you can hook him on interesting visual programming projects that require passing around functions as data (like creating a calculator or a model of a computer).

The manual explains how to write an object-oriented system in Snap, so you're really not going to be holding the kid back if you can get him in that way.

The iterated function systems also look cool and can be approached that way. The Beauty and Joy of Computing curriculum has a decently broad and intellectually challenging selection of project that can be done in Snap.

EDIT: I believe Snap can make calls to REST interfaces; you could write the back end and he could do the front end calls and use the data.