Quote from rickty:
Yannis,
What is your reason that you want to teach your kid to trade? And then the next question is, what sort of trader do you want him to be?
Most traders appear to be discretionary or technical traders. To my way of thinking this is akin to acquiring skill playing video games, as someone already mentioned above. In this sense I would encourage him to "play" the stock market rather than video games. But I would certainly not use any real money until he has proven himself.
If it was my kid, I would also introduce him to strategy trading. This could also introduce him to other more technical areas, such as computer programing and further down the road, signal processing and time series analysis. These may be areas he may wish to pursue in college.
Richard