The girls got the chance to play with some Ozobots recently. They respond to the colour and path of whatever line you place them on, so they will move along the path and change colour or direction depending on the colours they pass over.
The bots come with some pre-printed cards and you can download games for tablets but the most fun for our 3 and 5 year olds was to draw their own. The lines need to be fairly thick to work but they soon got the hang of it.
I tried to draw a path with loops (physical not code) to see if the ozobots could write a name but these little guys want to follow the easy path and got confused by the crossroads.
If you think of any other ideas to try please let me know!