The LittleBot robotics kit was created to be a simple introduction to robotics. It shows all the necessary components of robotics, sensing, decision-making, and articulation all in a nice, easy to assemble package.
The LittleBot is fully 3D printed, which allows it to be assembled with only 3 screws (7 if you are being over-zealous). It is also controlled by and Arduino Nano, to take advantage of the global community around that.
The LittleBot has several modes normally, including wander, remote-control (with android app), line follow, and wall follow. Code for all of these are available on the downloads page of the LittleBots website.
LittleBot was fully funded on Kickstarter in the middle of 2017 and recently completed deliveries. The kits are now available on the LittleBots website.
All of the 3D printing files for the LittleBot are available on thingiverse. The Arduino Code is on the LittleBots download page.
There are several expansions of the Littlebot that can be added to go even deeper into robotic and programming.