A pi + a full kit like breadboard/cables, LCD/LED display panels, camera, microphone/speaker, air sensors, IR sensors, gyros, etc. Now that's got a chance.
It's certainly not going to be for all kids but for those with an inquisitive mind once you set them up and show how to display output in various ways they will start to see the potential. From there you can move onto basic rc hobbyist stuff which is more accessible than ever. Buy some cheap brushless motors, wheels and a frame online, make the pi follow you around by sound only.