Try this :
The chocolate factory
Your kid will love it.
Now as a Belgian, I recommend the Galler chocolate. they have two shops. One in front of the carrefour at suntec and another one at Raffles city next to the Jasons supermarket.
The galler brand is THE chocolate if you want quality. They are in fact an official supplier to the King of Belgium to say the least.
Or you can bring him to the golden mile Food Court. A friend opened a Ang Moh Dessert stall with belgian waffles and chocolate fondue. It is really delicious and value for money.
See Here
If you need more info, just pm me.
Good luck and have fun with your kid !