I built a car with 4 DC motors, control it using a TV remote control which emits IR (Infra Red) signal. The IR signal was captured by the IR sensor on the car. Based on the button pressed on the remote control an Arduino program controlled the speed of the motors. This made the car move in different directions. It was not too complicated, but was fun to build.
As the name says, connecting them is a snap and fun. Would very much recommend for those who want to get their kids started with electronics.