We tried to build something fun and educative for our children. Although we love raspberry pi and other educational toy they can be rather overwhelming and overly complicated for very young children so we aimed for something simpler and tried stay away from screens as much as possible. We wanted it to be very tangible and only use things that can be found in every house. And we managed to get regular Lego bricks online using just an old mobile phone!
The concept is purposely very simple so that even a small child can grasp it. Bricks of different colors can trigger different sound but also trigger actions on the web. In the app you just configure which colour does what.
Using this app first we built a fun music player - compose a song using Lego bricks and then slide through the music machine.
As a bit more fun example we created Lego car race with live time board. Again same app with the mobiles hidden in Lego cars but this time the car not only makes engine noise depending on the surface it drives on but it also triggers web actions through the PubNub API and that gets pushed in real time to a static HTML page that shows lap times. And if your child has high tech bedroom with smart light bulbs you can add a tunnel section a turn off the lights in the room by triggering IFTTT actions.