I always used to start my students with a bendy wire game. The one where you have a loop (ground) and try to get from one end to the other without touching the wire (signal ). You can make it from a wire coat hanger and a block of wood.
The great thing is that it is so easy to expand it. Just start with an LED lighting up when it is touched, then a buzzer. Then have it latching on rather than momentary.
Then add end stops (two more inputs) so you can reset the LED and then time the run. Transfer the time to processing, have a high score table. Have touches add a 5 second penalty. The variations you can build are endless.